Int. Journal of Refractory Metals Hard Materials 27(2009)734-739 Contents lists available at Science Direct Int. Journal of Refractory Metals Hard Materials ELSEVIER journalhomepagewww.elsevier.com/locate/ijrmhm Design, fabrication and performance of Al2O3 /(Wo.7T10)C+ Al2O3/ TIC multilayered ceramic nozzles Deng Jianxin D,, Yun Dongling, Tan Yuanqiang ool of Mechanical Engineering, Xiangtan University, Xiangtan 411105, Hunan Province, PR China b School of Mechanical Engineering. Shandong University Jinan 250061, Shandong Province, PR China ARTICLE INF O A BSTRACT Article histo Al2O3/Wo.7Tio3)C+Al2O3 Tic multilayered ceramic nozzles(Nl, N2, N3 and N4 )with different thickness Received 2 August 2008 ratios among constituent layers were produced by hot-pressing. The value of the residual stress inside the Accepted 11 December 2008 layered nozzle during fabricating process was calculated by means of the finite element method. The mechanical properties at the surface layer of these layered materials were measured, the microstructure was examined. The wear behaviors of the multilayered nozzles were investigated and compared with an unstressed reference nozzle(N5). Results showed that the multilayered nozzles had superior erosion Nozzles wear resistance to that of the stress free one. The erosion wear resistance of the layered nozzles was Ceramic materials influenced by the thickness ratio among constituent layers. The N4 nozzle with thickness ratio of two Layered materials between adjacent layers exhibited higher erosion wear resistance over the nl N2 and N3 nozzles. Al203 e 2008 Elsevier Ltd. All rights reserved. 1 Introduction axial direction of the nozzle decreases from e and increases from center to exit. the highest tensile Laminated hybrid structures constituted by alternate layers are located on the entry section of the nozzle [13, 1 with different compositions can be properly designed to induce a authors previous studies [15-18. the idea of laminated struc urface compressive residual stress [1-4 The basic idea is to cou- tures was firstly introduced to the design of ceramic nozzles so ple material layers with different thermal expansion coefficients as to form compressive residual stresses at the nozzle (CtE)so that residual stresses arise during cooling from the sinter- exit)region in fabricating process, which may partially ing temperature Residual stresses arise from a mismatch between act the tensile stresses resulting from external loadings the Cte, sintering rates and elastic constants of the constituent showed that laminated structures in Sic/(W, Ti)C nozzle can in- phases and neighbouring layers, and the residual stress field de- duce an excess residual stress in the nozzle during fabricating pends on the geometry of the layered structure and on the thick- process, and this residual stress at the nozzle entry zone is com- ess ratio among layers [5-8. The design of ceramic laminates pressive whatever the sintering temperature [16]. This kind has been proved to be a viable strategy to obtain significant in- compressive residual stress can result in an improved erosion reases of the fracture resistance of ceramic materials. The effec wear resistance of the laminated nozzle compared with the tiveness of laminated structures in oving the tribological homologous stress-free one. properties has been also reported 9, 10. Toschi et al [11]reported In the present study, Al 2O3/(Wo.7Tio3) C+ Al2O3 TiC multilay- that laminated hybrid structures can improve the sliding wear ered ceramic nozzles with different thickness ratios among constit- sistance of alumina de portu et al. [12 showed that laminated uent layers were produced by hot-pressing in order to induce structures with compressive residual stresses within the surface compressive residual stress both at the entry and at the exit re egions were a suitable way to obtain composite materials with gions. The residual stress inside the layered nozzles during the sin- superior tribological properties tering process was calculated by means of the finite element The nozzle entrance section suffers severe abrasive impact, method(FEM). The mechanical properties at the surface layers of and generates the largest tensile stress. The stresses along the the layered materials were measured, the microstructure was examined. The wear behaviors of the multilayered nozzles were investigated and compared with an unstressed reference nozzle Particular attention was paid to the effect of thickness ratio among Address: School of Mechanical Engineering. shar vear behaviors of Al2O3/(Wo.7Tio3)C+ andong province, PR China Tel. +86 0531 8839 ndong constituent layers on the w Al2O3/TiC multilayered nozzles 0263-4368/s- see front matter o 2008 Elsevier Ltd. All rights reserved. do:101016 ijrmhm2008.12004
Design, fabrication and performance of Al2O3/(W0.7Ti0.3)C + Al2O3/TiC multilayered ceramic nozzles Deng Jianxin a,b,*, Yun Dongling b , Tan Yuanqiang a a School of Mechanical Engineering, Xiangtan University, Xiangtan 411105, Hunan Province, PR China b School of Mechanical Engineering, Shandong University, Jinan 250061, Shandong Province, PR China article info Article history: Received 2 August 2008 Accepted 11 December 2008 Keywords: Nozzles Residual stress Ceramic materials Layered materials Al2O3 abstract Al2O3/(W0.7Ti0.3)C + Al2O3/TiC multilayered ceramic nozzles (N1, N2, N3 and N4) with different thickness ratios among constituent layers were produced by hot-pressing. The value of the residual stress inside the layered nozzle during fabricating process was calculated by means of the finite element method. The mechanical properties at the surface layer of these layered materials were measured, the microstructure was examined. The wear behaviors of the multilayered nozzles were investigated and compared with an unstressed reference nozzle (N5). Results showed that the multilayered nozzles had superior erosion wear resistance to that of the stress-free one. The erosion wear resistance of the layered nozzles was influenced by the thickness ratio among constituent layers. The N4 nozzle with thickness ratio of two between adjacent layers exhibited higher erosion wear resistance over the N1, N2 and N3 nozzles. 2008 Elsevier Ltd. All rights reserved. 1. Introduction Laminated hybrid structures constituted by alternate layers with different compositions can be properly designed to induce a surface compressive residual stress [1–4]. The basic idea is to couple material layers with different thermal expansion coefficients (CTE) so that residual stresses arise during cooling from the sintering temperature. Residual stresses arise from a mismatch between the CTE, sintering rates and elastic constants of the constituent phases and neighbouring layers, and the residual stress field depends on the geometry of the layered structure and on the thickness ratio among layers [5–8]. The design of ceramic laminates has been proved to be a viable strategy to obtain significant increases of the fracture resistance of ceramic materials. The effectiveness of laminated structures in improving the tribological properties has been also reported [9,10]. Toschi et al. [11] reported that laminated hybrid structures can improve the sliding wear resistance of alumina. de Portu et al. [12] showed that laminated structures with compressive residual stresses within the surface regions were a suitable way to obtain composite materials with superior tribological properties. The nozzle entrance section suffers severe abrasive impact, and generates the largest tensile stress. The stresses along the axial direction of the nozzle decreases from entry to center, and increases from center to exit. The highest tensile stresses are located on the entry section of the nozzle [13,14]. In the author’s previous studies [15–18], the idea of laminated structures was firstly introduced to the design of ceramic nozzles so as to form compressive residual stresses at the nozzle entry (or exit) region in fabricating process, which may partially counteract the tensile stresses resulting from external loadings. Results showed that laminated structures in SiC/(W, Ti)C nozzle can induce an excess residual stress in the nozzle during fabricating process, and this residual stress at the nozzle entry zone is compressive whatever the sintering temperature [16]. This kind of compressive residual stress can result in an improved erosion wear resistance of the laminated nozzle compared with the homologous stress-free one. In the present study, Al2O3/(W0.7Ti0.3)C + Al2O3/TiC multilayered ceramic nozzles with different thickness ratios among constituent layers were produced by hot-pressing in order to induce a compressive residual stress both at the entry and at the exit regions. The residual stress inside the layered nozzles during the sintering process was calculated by means of the finite element method (FEM). The mechanical properties at the surface layers of the layered materials were measured, the microstructure was examined. The wear behaviors of the multilayered nozzles were investigated and compared with an unstressed reference nozzle. Particular attention was paid to the effect of thickness ratio among constituent layers on the wear behaviors of Al2O3/(W0.7Ti0.3)C + Al2O3/TiC multilayered nozzles. 0263-4368/$ - see front matter 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijrmhm.2008.12.004 * Corresponding author. Address: School of Mechanical Engineering, Shandong University, Jinan 250061, Shandong Province, PR China. Tel.: +86 0531 88392047. E-mail address: jxdeng@sdu.edu.cn (D. Jianxin). Int. Journal of Refractory Metals & Hard Materials 27 (2009) 734–739 Contents lists available at ScienceDirect Int. Journal of Refractory Metals & Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM
D Jianxin et al/Int. Journal of Refractory Metals E Hard Materials 27(2009)734-739 2. Materials and experimental procedure where Vi is the nozzle volume loss, w has the units of volume loss per unit mass(mm/g). 2.1. Preparation of the Al2O/Wo.7Ti03)C+ Al2Oa/TiC layered ceramic The finite element method (FEM) sed numerically evaluating the residual stress and its distribution within the layered nozzle in the fabricating processes The dimension and compositional distribution of the layered For observation of the micro-damage and determination of ero- ceramic nozzles with different thickness ratios among constituent sion mechanisms, the worn nozzles were sectioned axially. The layers are shown in Fig. 1. These nozzles possess a three-layer eroded bore surface of the nozzles was examined by scanning elec symmetrical structure. The composition at the nozzle entry and tron mi exit is Al203 45 voL%(Wo. 7Tio.3) C, while the composition at the nozzle center area is Al203 55 vol% TiC. Four layered nozzles with 3 Results and discussion different thickness ratio p(p=Al Az) among constituent layers were produced. The layered nozzles with the thickness ratio of 3. 1. Residual stress in the Al203/(Wa.7Tio3)C+Al203/Tic layered nozzle 0. 2, 0.5, 1 and 2 are named Nl, N2, N3 and N4, respectively(see The residual stress of the layered ceramic nozzles during fabri- The starting powders used to fabricate the layered nozzles are cating process was calculated by means of the finite element meth- listed in Table 1 with their physical properties. Composite powders od by assuming that the compact is cooled from sintering of different mixture ratios were prepared by wet ball milling temperature 1700C to room temperature 20C. The physical alcohol with cemented carbide balls for 80 h, respectively. Follow- properties of Al2O3, (Wo.7Tio.)C and TiC are listed in Table 1 ing drying, the composite powders with different mixture ratios Owing to the symmetry, an axisymmetric calculation was pre were layered into the graphite mould in turn. The sample was then ferred. Presume that it was steady state boundary condition. The hot-pressed in flowing nitrogen for 15 min at 1700C temperature results of the distribution of axial (oz)and radial(o)residual stres with 30 MPa pressure. For the purpose of comparison, a homolo- ses in the N2 layered nozzle in fabricating process from sintering gous stress-free ceramic nozzle was also manufactured by hot- temperature 1700C to room temperature 20C is shown in pressing. This stress-free nozzle made from A203 /45 voL% Fig. 2. It is indicated that an excess residual stress is formed both (Wo7Tio3)C is named N5 Layered structures constituted by alternate layers with different 2. 2. Abrasive air-jet machining compositions can be properly designed to induce a surface com- pressive residual stress. These residual stresses mainly arise from ressure was set at 0.4 MPa. The erodent abrasives used were of among layers [5-8]. Compressive residual stresses are induced in A203 powders with 150-250 um grain size. The mass loss of the layers with lower CTE, while tensile stresses arise in those with yorn ceramic nozzle was measured with a balance(minimum higher CTE. As for Al2O3/(Wo.7Tio3)C+Al2O3/TiC layered material 0.01 mg). Nozzles with internal diameter 8 mm and length the CTE of Al203/Wo.7Tio3)C is 7.2 x 10-K- and the CTE of 30 mm made from layered structure(Nl, N2, N3 and N4)and Al 03/TiC is 8.0 x 10-6K-I. That is to say, the thermal expansion stress-free structure(N5)were manufactured by hot-pressing. All coefficient of the entry section(surface layer)of the layered nozzle the test conditions are listed in table 2 The erosion rates(W) of the nozzles are defined as the nozzle stresses will be formed in the nozzle entry region during fabricat mass loss(mn)divided by the nozzle density (di) times the mass ing process of the erodent abrasive particles(m2) Fig 3 shows the residual stresses (oz and or)inside the N1, N2. (1) N and N4 layered nozzles at the inner-hole surtace along the noz. (20mn Al O,(W,Ti)c AhOLiC b) Fig. 1. Dimension and compositional distribution of the layered ceramic nozzles with different thickness ratios among constituent layers, (a)NI nozzle (p=0.2).(b)N2 ozzie(p=0.5. (c)N3 nozzle(p=1)and(d)N4 nozzle(p=2)
2. Materials and experimental procedures 2.1. Preparation of the Al2O3/(W0.7Ti0.3)C + Al2O3/TiC layered ceramic nozzles The dimension and compositional distribution of the layered ceramic nozzles with different thickness ratios among constituent layers are shown in Fig. 1. These nozzles possess a three-layer symmetrical structure. The composition at the nozzle entry and exit is Al2O3/45 vol.% (W0.7Ti0.3)C, while the composition at the nozzle center area is Al2O3/55 vol.% TiC. Four layered nozzles with different thickness ratio p (p = A1/A2) among constituent layers were produced. The layered nozzles with the thickness ratio of 0.2, 0.5, 1 and 2 are named N1, N2, N3 and N4, respectively (see Fig. 1). The starting powders used to fabricate the layered nozzles are listed in Table 1 with their physical properties. Composite powders of different mixture ratios were prepared by wet ball milling in alcohol with cemented carbide balls for 80 h, respectively. Following drying, the composite powders with different mixture ratios were layered into the graphite mould in turn. The sample was then hot-pressed in flowing nitrogen for 15 min at 1700 C temperature with 30 MPa pressure. For the purpose of comparison, a homologous stress-free ceramic nozzle was also manufactured by hotpressing. This stress-free nozzle made from Al2O3/45 vol.% (W0.7Ti0.3)C is named N5. 2.2. Abrasive air-jet machining The erosion wear tests were conducted with a GS-6 type abrasive air-jet machining machine tool [14]. The compressed air pressure was set at 0.4 MPa. The erodent abrasives used were of Al2O3 powders with 150–250 lm grain size. The mass loss of the worn ceramic nozzle was measured with a balance (minimum 0.01 mg). Nozzles with internal diameter 8 mm and length 30 mm made from layered structure (N1, N2, N3 and N4) and stress-free structure (N5) were manufactured by hot-pressing. All the test conditions are listed in Table 2. The erosion rates (W) of the nozzles are defined as the nozzle mass loss (m1) divided by the nozzle density (d1) times the mass of the erodent abrasive particles (m2): W ¼ m1=ðd1 m2Þ ¼ V1=m2 ð1Þ where V1 is the nozzle volume loss, W has the units of volume loss per unit mass (mm3 /g). The finite element method (FEM) was used as a means of numerically evaluating the residual stress and its distribution within the layered nozzle in the fabricating processes. For observation of the micro-damage and determination of erosion mechanisms, the worn nozzles were sectioned axially. The eroded bore surface of the nozzles was examined by scanning electron microscopy (SEM). 3. Results and discussion 3.1. Residual stress in the Al2O3/(W0.7Ti0.3)C + Al2O3/TiC layered nozzle The residual stress of the layered ceramic nozzles during fabricating process was calculated by means of the finite element method by assuming that the compact is cooled from sintering temperature 1700 C to room temperature 20 C. The physical properties of Al2O3, (W0.7Ti0.3)C and TiC are listed in Table 1. Owing to the symmetry, an axisymmetric calculation was preferred. Presume that it was steady state boundary condition. The results of the distribution of axial (rz) and radial (rr) residual stresses in the N2 layered nozzle in fabricating process from sintering temperature 1700 C to room temperature 20 C is shown in Fig. 2. It is indicated that an excess residual stress is formed both at the entry and the exit of the layered nozzle. Layered structures constituted by alternate layers with different compositions can be properly designed to induce a surface compressive residual stress. These residual stresses mainly arise from a mismatch between the coefficient of thermal expansion (CTE) of the constituent layers, and are influenced by the thickness ratio among layers [5–8]. Compressive residual stresses are induced in layers with lower CTE, while tensile stresses arise in those with higher CTE. As for Al2O3/(W0.7Ti0.3)C + Al2O3/TiC layered material, the CTE of Al2O3/(W0.7Ti0.3)C is 7.2 106 K1 and the CTE of Al2O3/TiC is 8.0 106 K1 . That is to say, the thermal expansion coefficient of the entry section (surface layer) of the layered nozzle is lower than that of the center layer, so that compressive residual stresses will be formed in the nozzle entry region during fabricating process. Fig. 3 shows the residual stresses (rz and rr) inside the N1, N2, N3 and N4 layered nozzles at the inner-hole surface along the nozzle axial direction in fabricating process. It is indicated that rz and (a) (b) (c) (d) A1 A2 A1 30 mm Al2O3/(W,Ti)C Al2O3/TiC Al2O3/(W,Ti)C Entry Exit Φ20mm Φ8mm Fig. 1. Dimension and compositional distribution of the layered ceramic nozzles with different thickness ratios among constituent layers, (a) N1 nozzle (p = 0.2), (b) N2 nozzle (p = 0.5), (c) N3 nozzle (p = 1) and (d) N4 nozzle (p = 2). D. Jianxin et al. / Int. Journal of Refractory Metals & Hard Materials 27 (2009) 734–739 735
736 D. Jianxin et aL/Int. Journal of Refractory Metals 8 Hard Materials 27(2009)734-739 Physical properties of AlzO3, TiC and(wozTio3)c arting Density Youngs modulus Thermal expansion coefficient Thermal Poissons Particle size Purity Manufacture (g/cm)(GPa) (10-6K-1) inductivity rato Al,O3 3.98 Beijing Antai Advanced Tech. an Zhuzhou cemented ca WozTioa)c 9.5 214 Zhuzhou cemented ca works Fracture toughness measurement was performed using inden- tation method at the nozzle surface layer(nozzle entry )in a hard- Abrasive air-jet equipment GS-6 type abrasive air-jet machine tool ness tester(MH 6) using the formula proposed by Cook and Lawn Nozzle material Ni, N2, N3 and N4 layered nozzles [19]. Hardness measurements were performed by placing Vickers indentations on surface layer of the layered nozzle material. The 0-250 um Al2O3 powders indentation load was 200n and a minimum of five indentations were tested. The Vickers hardness(GPa)is given by Cumulative mass weigh Balance(minimum 0.01 mg H ar residual stresses at the nozzle entry or exit area are all compres- where P is the indentation load (N), and 2a is the catercorner length sive whatever the thickness ratios. The Ni layered nozzle with (um)due to indentation. thickness ratio of 0.2 among constituent layers had the highest The results of hardness and fracture toughness of the layered compressive stress(-315 MPa)at the nozzle entry; while the n4 nozzle with different thickness ratios among constituent layers nozzle with thickness ratio of two had the smallest compressive are presented in Table 3. It is indicated that the hardness and frac stress(-24 4 MPa)at the nozzle entry Therefore, layered struc- ture toughness decrease gradually from NI nozzle to N5 nozzle. tures in these ceramic nozzles can form an excess compressive The external layer(nozzle entry or exit) of the nozzle with low residual stresses at the nozzle entry(or exit)area during fabricat- thickness ratio shows the highest hardness and fracture toughness ng process. The smaller the thickness ratio, the higher the com- By comparison with the stress-free nozzle(N5). the hardness at the pressive stress at the nozzle entry or exit area. external layer of the layered nozzles is much more improved, and From Fig. 3, we can also see that the radial residual stress or rose from 19. 9 GPa for N5 stress-free nozzle to 21.6 GPa for NI lay- showed no much change along the nozzle axial direction for ered nozzle, representing a maximum increase of 1.7 GPa. While Al2O3/Wo.7Tio3)C+Al203TiC layered material The reason is that the fracture toughness rose from 4.9 MPa m/2 for N5 stress-free multilayered material (the compositions are only changed in noz- imum increase of 4.9 MPa m e Vered nozzle, representing a max- the compositions in nozzle radial direction are the same for this nozzle to 9.8 MPa m for NI la zle axial direction, see Fig. 1) so there is no difference in thermal As can be that layered structures in Al2O3/(Wo.Tio3)C+ expansion coefficient in the nozzle radial direction, which leads Al203/TiC material can form an excess compressive residual stress to almost identical radial residual stress o, along the nozzle axial at the nozzle entry (or exit area during fabricating process. The direction smaller the thickness ratio, the higher the compressive stress at he nozzle entry or exit area. These compressive residual stresses ructural characterization and surface layer properties of are benefit for the increase of hardness and the fracture toughne AlyO3 lo3)C+ Al,O TiC layered nozzle materials at the surface layer of the layered structures, which is also reported by other researchers [1-4 The high hardness and fracture tough- The SEM micrographs of the cross-section surface of the N4 lay- ness of the layered nozzles with low thickness ratios among con- ered nozzle material are shown in Fig 4. a layered structure can be stituent layers may attribute to their high compressive stresses clearly seen. at the external layer (entry or exit ) b -320-261-203-14485-263190149 Fig.2. Distribution of (a)axial residual stress dz and (b)radial residual stress dr in N2 layered nozzle during fabricating process from sintering temperature 1700Cto
rr residual stresses at the nozzle entry or exit area are all compressive whatever the thickness ratios. The N1 layered nozzle with thickness ratio of 0.2 among constituent layers had the highest compressive stress (31.5 MPa) at the nozzle entry; while the N4 nozzle with thickness ratio of two had the smallest compressive stress (24.4 MPa) at the nozzle entry. Therefore, layered structures in these ceramic nozzles can form an excess compressive residual stresses at the nozzle entry (or exit) area during fabricating process. The smaller the thickness ratio, the higher the compressive stress at the nozzle entry or exit area. From Fig. 3, we can also see that the radial residual stress rr showed no much change along the nozzle axial direction for Al2O3/(W0.7Ti0.3)C + Al2O3/TiC layered material. The reason is that the compositions in nozzle radial direction are the same for this multilayered material (the compositions are only changed in nozzle axial direction, see Fig. 1), so there is no difference in thermal expansion coefficient in the nozzle radial direction, which leads to almost identical radial residual stress rr along the nozzle axial direction. 3.2. Microstructural characterization and surface layer properties of Al2O3/(W0.7Ti0.3)C + Al2O3/TiC layered nozzle materials The SEM micrographs of the cross-section surface of the N4 layered nozzle material are shown in Fig. 4. A layered structure can be clearly seen. Fracture toughness measurement was performed using indentation method at the nozzle surface layer (nozzle entry) in a hardness tester (MH 6) using the formula proposed by Cook and Lawn [19]. Hardness measurements were performed by placing Vickers indentations on surface layer of the layered nozzle material. The indentation load was 200 N and a minimum of five indentations were tested. The Vickers hardness (GPa) is given by: Hv ¼ 1:8544 P ð2aÞ 2 ð2Þ where P is the indentation load (N), and 2a is the catercorner length (lm) due to indentation. The results of hardness and fracture toughness of the layered nozzle with different thickness ratios among constituent layers are presented in Table 3. It is indicated that the hardness and fracture toughness decrease gradually from N1 nozzle to N5 nozzle. The external layer (nozzle entry or exit) of the nozzle with low thickness ratio shows the highest hardness and fracture toughness. By comparison with the stress-free nozzle (N5), the hardness at the external layer of the layered nozzles is much more improved, and rose from 19.9 GPa for N5 stress-free nozzle to 21.6 GPa for N1 layered nozzle, representing a maximum increase of 1.7 GPa. While the fracture toughness rose from 4.9 MPa m1/2 for N5 stress-free nozzle to 9.8 MPa m1/2 for N1 layered nozzle, representing a maximum increase of 4.9 MPa m1/2. As can be seen that layered structures in Al2O3/(W0.7Ti0.3)C + Al2O3/TiC material can form an excess compressive residual stress at the nozzle entry (or exit) area during fabricating process. The smaller the thickness ratio, the higher the compressive stress at the nozzle entry or exit area. These compressive residual stresses are benefit for the increase of hardness and the fracture toughness at the surface layer of the layered structures, which is also reported by other researchers [1–4]. The high hardness and fracture toughness of the layered nozzles with low thickness ratios among constituent layers may attribute to their high compressive stresses at the external layer (entry or exit). Table 1 Physical properties of Al2O3, TiC and (W0.7Ti0.3)C. Starting powder Density (g/cm3 ) Young’s modulus (GPa) Thermal expansion coefficient (106 K1 ) Thermal conductivity (W/m K) Poisson’s ratio Particle size (lm) Purity (%) Manufacture Al2O3 3.98 380 8.0 30.2 0.27 1–2 >99 Beijing Antai Advanced Tech. and Mater. Co., Ltd. TiC 4.93 500 7.4 24.3 0.20 1–2 >99 Zhuzhou cemented carbide works (W0.7Ti0.3)C 9.56 480 8.5 21.4 0.25 1–2 >99 Zhuzhou cemented carbide works Table 2 Abrasive air-jet machining conditions. Abrasive air-jet equipment GS-6 type abrasive air-jet machine tool Nozzle material N1, N2, N3 and N4 layered nozzles N5 stress-free nozzle Dimension of the nozzles U 8 mm (internal diameter) 30 mm (length) Erodent abrasives 150–250 lm Al2O3 powders Compressed air pressure 0.4 MPa Cumulative mass weigh Balance (minimum 0.01 mg) -320 -261 -203 -144 -85 -26 31 90 149 (MPa) (MPa) -290 -226 -162 -98 -34 29 92 156 220 a b Fig. 2. Distribution of (a) axial residual stress rz and (b) radial residual stress rr in N2 layered nozzle during fabricating process from sintering temperature 1700 C to room temperature 20 C. 736 D. Jianxin et al. / Int. Journal of Refractory Metals & Hard Materials 27 (2009) 734–739
D Jianxin et al/ Int. Journal of Refractory Metals E Hard Materials 27(2009)734-739 a300 b -Radial stress )- Axial stress Radial stress ● Ent Center layer yer Center layer Nozzle axial direction(mm) Nozzle axial direction(mm) 。- Axial stress O- Axial stress 0- Radial stress Radial stress l00 ●●鲁● ●●●●●4● 100 Center layer Entry la 200 12 Fig 3. The resi esses of the layered nozzle with different layer thickness ratios at the inner-hole surface along the nozzle axial direction, (a)Ni nozzle (p=0.2).(b)N2 ozzie (p=0.5).(c)N3 nozzle (p= 1)and( d)N4 nozzle (p=2 c b d 2mm[, 4. SEM micrographs of the cross-section surface of the N4 layered nozzle material. Hardness and fracture toughness at the surface layer(nozzle entry) of the layered ceramic nozzles with different thickness ratios among constituent layers. Hardness(GPa) Fracture toughness(MPa m2) ±12 98±0.6 21.1±1.1 84±0. vered nozzle 09±1.1 7.3±0.5 N4 layered nozzle 206±1.0 5.8±04 N5 stress-free nozzle 199±1.0 4.9±0.5
-200 -100 0 100 200 300 0 3 6 9 12 15 Nozzle axial direction (mm) Radial stress (MPa) Axial stress Radial stress Entry layer Center layer -200 -100 0 100 200 300 0 3 6 9 12 15 Nozzle axial direction (mm) Radial stress (MPa) Axial stress Radial stress Entry layer Center layer -200 -100 0 100 200 300 0 3 6 9 12 15 Nozzle axial direction (mm) Radial stress (MPa) Radial stress Axial stress Entry layer Center layer -200 -100 0 100 200 300 0 3 6 9 12 15 Nozzle axial direction (mm) Radial stress (MPa) Axial stress Radial stress Entry layer Center layer a b c d Fig. 3. The residual stresses of the layered nozzle with different layer thickness ratios at the inner-hole surface along the nozzle axial direction, (a) N1 nozzle (p = 0.2), (b) N2 nozzle (p = 0.5), (c) N3 nozzle (p = 1) and (d) N4 nozzle (p = 2). 2mm 150μm 15μm 15μm Entry layer Center layer Exit layer a b c d Fig. 4. SEM micrographs of the cross-section surface of the N4 layered nozzle material. Table 3 Hardness and fracture toughness at the surface layer (nozzle entry) of the layered ceramic nozzles with different thickness ratios among constituent layers. Code name Thickness ratio p = A1/A2 Hardness (GPa) Fracture toughness (MPa m1/2) N1 layered nozzle 0.2 21.6 ± 1.2 9.8 ± 0.6 N2 layered nozzle 0.5 21.1 ± 1.1 8.4 ± 0.5 N3 layered nozzle 1 20.9 ± 1.1 7.3 ± 0.5 N4 layered nozzle 2 20.6 ± 1.0 5.8 ± 0.4 N5 stress-free nozzle 19.9 ± 1.0 4.9 ± 0.5 D. Jianxin et al. / Int. Journal of Refractory Metals & Hard Materials 27 (2009) 734–739 737
738 D. Jianxin et aL/Int. Journal of Refractory Metals 8 Hard Materials 27(2009)734-739 3.3. Erosion wear of the Al2O,/Wo. 7Ti03)C+Al2O /TiC layered ceramic with thickness ratio of two among constituent layers had the smallest erosion wear rate. Therefore, it is apparently that the lay ered nozzles exhibited higher erosion wear resistance over the Fig 5 shows the comparison of the erosion rates of N1, N2, N3 stress-free one, and the layered nozzles with high thickness ratio and N4 layered and N5 stress-free nozzle in abrasive air- showed the low erosion wear rate ious that the erosion rate of the layered noz- The results of the nozzle entry bore diameter variation with the thestress-freeonethen4layerednozzleerosiontimeforN2,N4andn5nozzlesareshowninFig.6.com- pared with the layered nozzles, the entry bore diameter of the n5 stress-free nozzle enlarges greatly under the same test conditions. The worn ceramic nozzles were cut in longitudinal directio after o n for failure analysis. Fig. 7 shows the photos of the aN5 stress-free nozzle inner-hole profile of the whole ceramic nozzle after 540 min oper 日N4 layered nozzle ation. it is showed that inner-hole diameter of the stress-free noz. 口N3 layered nozzle Zle(n5)along the longitudinal direction is larger than that of the 口N2 layered nozzle layered one(N4), especially at the entry and exit regions. 口 NI layered nozzle 3. 4. Discussion Nozzle failure by erosion wear is usually accompanied by chip- ping at the entry [13, 14]. Because the nozzle entrance region suf- fers severe abrasive impact, and generates large tensile stress, which may cause the subsurface lateral cracks and facilitate the re- moval of the material chips. Thus, the erosion wear of the nozzle depends on the stress distribution in the entry and exit region. Once the maximum tensile stress exceeds the ultimate strength Fig. 5. Comparison of the erosion rates of the Ni, N2, N3 and N4 layered nozzles of the nozzle material, fracture will occur. and N5 stress-free nozzle in abrasive air-jet machining As calculated above, compressive residual stresses can be intro- duced at the entry (or exit) of the nozzle in cooling process from sintering temperature to room temperature when designed with symmetrical layered structures at its entry and exit. The higher erosion wear resistance of the layered nozzle(especially at the en try and exit of the nozzle) compared with the stress-free one can analysed in terms of these compressive residual stresses (se 3), which may partially counteract the tensile stresses at the try and exit of the nozzle resulting from external loadings. this effect can also lead to the increase in resistance to fracture. Conse- quently, the propagation of a crack generated during the erosion process can be considerably hindered, and thus increase the ero- sion wear resistance of the layered nozzle. N5 stress-free nozzle Among the four layered nozzles, the n4 nozzle with thickness ratio of two between adjacent layers exhibited higher erosion wear 0-N4 layered nozzle resistance over the nl, N2 and N3 nozzles(see Fig. 5). Although the layered nozzles with low thickness ratios(NI and N2) has higher surface hardness and fracture toughness (see Table 3). their surface layer (entry or exit) with compressive residual stresses is rather 80160240320400480 thin(see Fig. 3). Therefore, the erosion wear e of the lay- Erosion time(min) ered nozzles was influenced by the thickness mong con Fig. 6. Nozzle entry bore diameter variation with the erosion time for N2 and N4 uent layers. The layered nozzles with high thi ratio showed layered nozzles and N5 stress-free nozzle in abrasive air-jet machining high erosion wear resistance b Fig. 7. Photos of the worn inner-hole profile of (a) N4 layered nozzle and (b) N5 stress-free nozzle after 540 min operation
3.3. Erosion wear of the Al2O3/(W0.7Ti0.3)C + Al2O3/TiC layered ceramic nozzles Fig. 5 shows the comparison of the erosion rates of N1, N2, N3 and N4 layered nozzles and N5 stress-free nozzle in abrasive airjet machining. It is obvious that the erosion rate of the layered nozzle is lower than that of the stress-free one, the N4 layered nozzle with thickness ratio of two among constituent layers had the smallest erosion wear rate. Therefore, it is apparently that the layered nozzles exhibited higher erosion wear resistance over the stress-free one, and the layered nozzles with high thickness ratio showed the low erosion wear rate. The results of the nozzle entry bore diameter variation with the erosion time for N2, N4 and N5 nozzles are shown in Fig. 6. Compared with the layered nozzles, the entry bore diameter of the N5 stress-free nozzle enlarges greatly under the same test conditions. The worn ceramic nozzles were cut in longitudinal direction after operation for failure analysis. Fig. 7 shows the photos of the inner-hole profile of the whole ceramic nozzle after 540 min operation. It is showed that inner-hole diameter of the stress-free nozzle (N5) along the longitudinal direction is larger than that of the layered one (N4), especially at the entry and exit regions. 3.4. Discussion Nozzle failure by erosion wear is usually accompanied by chipping at the entry [13,14]. Because the nozzle entrance region suffers severe abrasive impact, and generates large tensile stress, which may cause the subsurface lateral cracks and facilitate the removal of the material chips. Thus, the erosion wear of the nozzle depends on the stress distribution in the entry and exit region. Once the maximum tensile stress exceeds the ultimate strength of the nozzle material, fracture will occur. As calculated above, compressive residual stresses can be introduced at the entry (or exit) of the nozzle in cooling process from sintering temperature to room temperature when designed with symmetrical layered structures at its entry and exit. The higher erosion wear resistance of the layered nozzle (especially at the entry and exit of the nozzle) compared with the stress-free one can be analysed in terms of these compressive residual stresses (see Fig. 3), which may partially counteract the tensile stresses at the entry and exit of the nozzle resulting from external loadings. This effect can also lead to the increase in resistance to fracture. Consequently, the propagation of a crack generated during the erosion process can be considerably hindered, and thus increase the erosion wear resistance of the layered nozzle. Among the four layered nozzles, the N4 nozzle with thickness ratio of two between adjacent layers exhibited higher erosion wear resistance over the N1, N2 and N3 nozzles (see Fig. 5). Although the layered nozzles with low thickness ratios (N1 and N2) has higher surface hardness and fracture toughness (see Table 3), their surface layer (entry or exit) with compressive residual stresses is rather thin (see Fig. 3). Therefore, the erosion wear resistance of the layered nozzles was influenced by the thickness ratio among constituent layers. The layered nozzles with high thickness ratio showed high erosion wear resistance. 0 0.5 1 1.5 2 2.5 Nozzles Erosion rate W (10-3mm3/g) N5 stress-free nozzle N4 layered nozzle N3 layered nozzle N2 layered nozzle N1 layered nozzle Fig. 5. Comparison of the erosion rates of the N1, N2, N3 and N4 layered nozzles and N5 stress-free nozzle in abrasive air-jet machining. 0 1 2 3 0 80 160 240 320 400 480 Erosion time (min) Bore diameter variation (mm) N5 stress-free nozzle N2 layered nozzle N4 layered nozzle Fig. 6. Nozzle entry bore diameter variation with the erosion time for N2 and N4 layered nozzles and N5 stress-free nozzle in abrasive air-jet machining. a Entry Exit Entry Exit Entry layer Center layer Exit layer b Fig. 7. Photos of the worn inner-hole profile of (a) N4 layered nozzle and (b) N5 stress-free nozzle after 540 min operation. 738 D. Jianxin et al. / Int. Journal of Refractory Metals & Hard Materials 27 (2009) 734–739
D Jianxin et al/Int. Journal of Refractory Metals E Hard Materials 27(2009)734-739 [2 Cai Pz, Green D], Messing GL I al characterization of Al2O3/Zro, hybrid minates. J Eur Ceram Soc 1998 5: 2025-34. Al2O3/(Wo.7Tio.3)C+ Al2O3/TiC [3 de Portu G, Micele L Pezzotti G. Laminated ceramic structures from oxide with different thickness ratios amd [4] Sglavo Vincenzo M, Bertoldi Massimo. Design and production of ceramic duced by hot-pressing. Particular 二 laminates with high mechanical resistance and reliability. Acta Mater landri C, Pezzotti G, Sciti D. Effects of residual 1-oxide laminated composites. J Eur (1) Multilayered structure can induce excess residual [6 Tomaszewski Henryk ena, Wailer Anna, Boniecki Marek, Kalinski both at the entry and the exit due to the different ram Soc2007;27:1373-7 expansion coefficients of the individual layers. The [7 Sergo V, Lipkin DM, de Portu G, Clarke DR Edge stresses in alumina zirconia ual stresses are all compressive whatever the 03 3Y-TZP multilane (2)The hardness and fracture toughness at the external lay cence and Raman microprobe piezo-spectroscopy. Acta Mater 2005 entry or exit) decrease gradually from NI nozzle to N5 noz- 191 Tarla ncari E, Pinasco P, Guicciardi S. Melandri C, de portu G. le, and the nozzle with low thickness ratio shows the high- ibological behaviour of AlzO3ZrOx-Zroz laminated comp Wear (3) The layered nozzles(N1, N2, N3 and N4) had superior ero- [10/ ha:244: 29-40 est surface hardness and fracture toughness. G, Kubler]. Rosset e, Rohr L, Michler ]. Tribological l sion wear resistance to that of the stress-free one(n of Si3N4 and Si3Na-% Tin based composites and multi-layer laminates. Wear cially at the entry and the exit. The erosion wear resistance [11] Toschi F, Melandri C, Pinasco P, Roncari E, Guicciardi S, de PortuG.Influence of was influenced by the thickness ratio omposites. J Am Ceram Soc 2003: 86(9): 1547-53. imong constituent layers. The N4 nozzle with thickness [12\ e cerax Erosion wed composites. wear 20062650: 1 04-11 atio of two between adjacent layers exhibited higher ero- sion wear resistance over the ni n2 and n3 nozzles [13] Deng J 14Dengⅸ Feng YH, Dir ram Acknowledgement [15] Den t ceramIc for sand blasting surface treatments. Int J Refract Met Hard This work was supported by"the Lotus Scholars Programme "the Key Science and Technology Project of Shandong Province [16 Deng JX, Liu Ll Ding Mw. Effect e (2006GG2204017) 9:I-gn the erosion wear of [17 Deng X, Liu LL, Dir 1209 in dry sand esses. Mater Sci Eng A References [18] Deng JX, Liu LL, Zhao JL Sun JL Erosion wear of laminated ceramic nozzles. Int J [1] Lakshminarayanan R, Shetty DK, Cutler RA Toughening of layered ceramic efrat Met hard mat 79-87>Ites with residual surface compression. J Am Ceram Soc 9:19 ed indentation toughness technique. J Am Ceram Soc1983:66(11)200-1
4. Conclusions Al2O3/(W0.7Ti0.3)C + Al2O3/TiC multilayered ceramic nozzles with different thickness ratios among constituent layers were produced by hot-pressing. Particular attention was paid on wear behaviors of these nozzles. The following conclusions were obtained: (1) Multilayered structure can induce excess residual stresses both at the entry and the exit due to the different thermal expansion coefficients of the individual layers. These residual stresses are all compressive whatever the thickness ratios. (2) The hardness and fracture toughness at the external layer (entry or exit) decrease gradually from N1 nozzle to N5 nozzle, and the nozzle with low thickness ratio shows the highest surface hardness and fracture toughness. (3) The layered nozzles (N1, N2, N3 and N4) had superior erosion wear resistance to that of the stress-free one (N5), especially at the entry and the exit. The erosion wear resistance of the layered nozzles was influenced by the thickness ratio among constituent layers. The N4 nozzle with thickness ratio of two between adjacent layers exhibited higher erosion wear resistance over the N1, N2 and N3 nozzles. Acknowledgement This work was supported by ‘‘the Lotus Scholars Programme”, ‘‘the Key Science and Technology Project of Shandong Province (2006GG2204017)”. References [1] Lakshminarayanan R, Shetty DK, Cutler RA. Toughening of layered ceramic composites with residual surface compression. J Am Ceram Soc 1996;79(1): 79–87. [2] Cai PZ, Green DJ, Messing GL. Mechanical characterization of Al2O3/ZrO2 hybrid laminates. J Eur Ceram Soc 1998;5:2025–34. [3] de Portu G, Micele L, Pezzotti G. Laminated ceramic structures from oxide systems. Comp Part B 2006;37:556–67. [4] Sglavo Vincenzo M, Bertoldi Massimo. Design and production of ceramic laminates with high mechanical resistance and reliability. Acta Mater 2006;54:4929–37. [5] Guicciardi S, Nagliati M, Melandri C, Pezzotti G, Sciti D. Effects of residual stresses on the fracture properties of non-oxide laminated composites. J Eur Ceram Soc 2007;27:351–6. [6] Tomaszewski Henryk, Weglarz Helena, Wajler Anna, Boniecki Marek, Kalinski Dariusz. Multilayer ceramic composites with high failure resistance. J Eur Ceram Soc 2007;27:1373–7. [7] Sergo V, Lipkin DM, de Portu G, Clarke DR. Edge stresses in alumina/zirconia laminates. J Am Ceram Soc 1997;80(7):1633–8. [8] de Portu G, Micele L, Sekiguchi Y, Pezzotti G. Measurements of residual stress distributions in Al2O3/3Y–TZP multilayered composites by fluorescence and Raman microprobe piezo-spectroscopy. Acta Mater 2005;53: 1511–20. [9] Tarlazzi A, Roncari E, Pinasco P, Guicciardi S, Melandri C, de Portu G. Tribological behaviour of Al2O3/ZrO2–ZrO2 laminated composites. Wear 2000;244:29–40. [10] Hadad M, Blugan G, Kübler J, Rosset E, Rohr L, Michler J. Tribological behaviour of Si3N4 and Si3N4–% TiN based composites and multi-layer laminates. Wear 2006;260:634–41. [11] Toschi F, Melandri C, Pinasco P, Roncari E, Guicciardi S, de Portu G. Influence of residual stress on the wear behaviour of alumina/alumina–zirconia laminated composites. J Am Ceram Soc 2003;86(9):1547–53. [12] de Portu G, Micele L, Prandstraller D, Palombarini G, Pezzotti G. Abrasive wear in ceramic laminated composites. Wear 2006;260:1104–11. [13] Deng JX. Erosion wear of boron carbide nozzles by abrasive air-jets. Mater Sci Eng A 2005;408(1–2):227–33. [14] Deng JX, Feng YH, Ding ZL. Wear behaviors of the ceramic nozzles in sand blasting treatments. J Eur Ceram Soc 2003;23:323–9. [15] Deng JX, Liu LL, Li JF, Ding MW, Yang XF. Development of gradient ceramic nozzle materials for sand blasting surface treatments. Int J Refract Met Hard Mater 2007;25:130–7. [16] Deng JX, Liu LL, Ding MW. Effect of residual stresses on the erosion wear of laminated ceramic nozzles. Mater Charact 2008;59:1–8. [17] Deng JX, Liu LL, Ding MW. Erosion wear behaviours of SiC/(W, Ti)C laminated ceramic nozzles in dry sand blasting processes. Mater Sci Eng A 2007;444:120–9. [18] Deng JX, Liu LL, Zhao JL, Sun JL. Erosion wear of laminated ceramic nozzles. Int J Refract Met Hard Mater 2007;25:263–70. [19] Cook RF, Lawn BR. A modified indentation toughness technique. J Am Ceram Soc 1983;66(11):200–1. D. Jianxin et al. / Int. Journal of Refractory Metals & Hard Materials 27 (2009) 734–739 739