ournal J.Am.Ceum.Soc.8104-1212004 Effect of a boron Nitride Interphase that Debonds between the Interphase and the matrix in SiC/SiC Composites Gregory N Morscher Ohio Aerospace Institue, Cleveland, Ohio 44142 Hee Mann yun*, Cleveland State University, Cleveland, Ohio 44115 James A. Dicarlo NASA Glenn Research Center. Cleveland, Ohio 44135 Linus Thomas-Ogbuji·t QSs Group, Inc, Cleveland, Ohio 44135 Typically, the debonding and sliding interface enabling fiber interfaces as well as oxidation of the fiber surface(Fig. 1(a). The pullout for SiC-fiber-reinforced SiC-matrix composites with liquid boria reaction product reacts with the Sic fiber to form a BN-based interphases occurs between the fiber and the inter borosilicate liquid that increases in SiO2 content with phase. Recently, composites have been fabricated where inter oxidation of the SiC. Also, B,, reacts with water vapor face debonding and sliding occur between the BN interphase atmosphere to form volatile B-containing hydrated species os result ind the matrix. This results in two major improvements in ing in an even higher Sio content in the oxidation product. These mechanical properties. First, significantly higher failure phenomena result in a solid oxidation product(glass) that strongly strains were attained due to the lower interfacial shear bonds fibers bridging the matrix crack to one another or to the strength with no loss in ultimate strength properties of the matrix itself and causes subsequent composite embrittlement( Fig composites. Second, significantly longer stress-rupture times at 1(a) higher stresses were observed in air at s15C. In addition, no One proposal to curtail this type of rapid oxidative process that loss in mechanical properties was observed for composites that leads to composite embrittlement would be for the debonding and did not possess a thin carbon layer between the fiber and th sliding interface to be some distance away from the reinforcing interphase when subjected to burner- rig exposure Two pri fibers. For SiC/SiC composites this has been attempted with mary factors were hypothesized for the occurrence of debond C/SiC multilayers as the"interphase"3-5 and more recently with ng and sliding between the bn interphase and the siC matrix: BN/SiC multilayers. In theory, debonding and sliding would a weaker interface at the BN/matrix interface than the fi- occur in some of the outer layers, prohibiting or complicating the ber/BN interface and a residual tensile/shear stress-state at the diffusion of oxidizing species to the inner fiber/interphase region BN/matrix interface of melt-infiltrated composites. Also, the that leads to composite embrittlement. Some benefit has been occurrence of outside debonding was believed to occur during demonstrated for stress-rupture of minicomposites with multilayer cooldown after molten silicon infiltration For SiC/SiC composites with Bn interphases, if the debonding and sliding layer was between the bn and the matrix, a similar benefit proposed for the multilayer approach could be I. Introduction Oxidation of the bn would occur from the"outside" f the bn OR woven SiC/Sic composites with BN interphases, the typical would react with the Sic matrix to eventually form a borosilicate interface where debonding and sliding occur is between the fI er and the bn interphase. We refer to this phenomenon glass that would act as a"sealant "slowing diffusion of oxidizing species to the Bn. In order for the fibers to be fused together or to interphase exacerbates the environmental durability problem of the mcat i:ioi dabo h s m en tr thiconsid er ble am wn of ae terphases at intermediate temper- considering the effects of sealing and the reduced surface area of atures(600 to 1000C)in the presence of oxidizing atmo- BN exposed to oxidizing species when compared with the typical direct access to the fibers themselves. This causes oxidation of the benefit expected from an outside debonded interphase in SiC/Sic Bn interphase preferentially at both the fiber/BN and BN/CVI SiC composites would be improved intermediate-temperature mechan ical properties, e. g, stress-rupture, in oxidizing environments Such behavior has been demonstrated and will be described and discussed in this work I. Experimental Procedure se NASA UF: 2002: approved April 23, 2003 0784 Received A SiC-fiber-reinforced melt-infiltrated SiC-matrix Ceram els that exhibited outside debonding were fabricated from 2D- cientist at NASA Glenn Research Center, Cleveland, OH woven, balanced, 5 harness satin, 0/90 fabric, by General ElectricJ. Am. Cerum. Soc., 87 [I] 104-12 (2004) journal Effect of a Boron Nitride lnterphase That Debonds between the lnterphase and the Matrix in SiC/SiC Composites Gregory N. Morscher*.+ Ohio Aerospace Institue, Cleveland, Ohio 44142 Hee Mann Yun*.t Cleveland State University, Cleveland, Ohio 44 I 15 James A. DiCarlo* NASA Glenn Research Center, Cleveland, Ohio 44135 Linus Thomas-Ogbuji*7t QSS Group, Inc., Cleveland, Ohio 44135 Typically, the debonding and I ding interface enabling fiber pullout for Sic-fiber-reinforced Sic-matrix composites with BN-based interphases occurs between the fiber and the inter￾phase. Recently, composites have been fabricated where inter￾face debonding and sliding occur between the BN interphase and the matrix. This results in two major improvements in mechanical properties. First, significantly higher failure strains were attained due to the lower interfacial shear strength with no loss in ultimate strength properties of the composites. Second, significantly longer stress-rupture times at higher stresses were observed in air at 815°C. In addition, no loss in mechanical properties was observed for composites that did not possess a thin carbon layer between the fiber and the interphase when subjected to burner-rig exposure. Two pri￾mary factors were hypothesized for the Occurrence of debond￾ing and sliding between the BN interphase and the Sic matrix: a weaker interface at the BNhatrix interface than the fi￾ber/BN interface and a residual tensilekhear stress-state at the BN/matrix interface of melt-infiltrated composites. Also, the occurrence of outside debonding was believed to occur during composite fabrication, i.e., on cooldown after molten silicon infiltration. I. Introduction OR woven SiClSiC composites with BN interphases, the typical F interface where debonding and sliding occur is between the fiber and the BN interphase. We refer to this phenomenon as “inside debonding.” Unfortunately, the inside debonding of the interphase exacerbates the environmental durability problem of SiC/SiC composites with BN interphases at intermediate temper￾atures (600” to lO00”C) in the presence of oxidizing atmo￾spheres.’.’ When matrix cracks are formed, the environment has direct access to the fibers themselves. This causes oxidation of the BN interphase preferentially at both the fiberlBN and BN/CVI Sic R. Naslain-ontributing editor Manuscript No. 186784. Received August 7, 2002: approved April 23,2003. This work was supported by the NASA UEET program. ‘Member, American Ceramic Society. ‘Senior Research Scientist at NASA Glenn Research Center, Cleveland, OH. interfaces as well as oxidation of the fiber surface (Fig. l(a)). The liquid boria reaction product reacts with the Sic fiber to form a borosilicate liquid that increases in SiO, content with further oxidation of the Sic. Also, B,O, reacts with water vapor in the atmosphere to form volatile B-containing hydrated species result￾ing in an even higher SiO, content in the oxidation product. These phenomena result in a solid oxidation product (glass) that strongly bonds fibers bridging the matrix crack to one another or to the matrix itself and causes subsequent composite embrittlement (Fig. One proposal to curtail this type of rapid oxidative process that leads to composite embrittlement would be for the debonding and sliding interface to be some distance away from the reinforcing fiber^.^ For SiC/SiC composites this has been attempted with C/SiC multilayers as the “interpha~e”~-~ and more recently with BN/SiC multilayers.6 In theory, debonding and sliding would occur in some of the outer layers, prohibiting or complicating the diffusion of oxidizing species to the inner fibedinterphase region that leads to composite embrittlement. Some benefit has been demonstrated for stress-rupture of minicomposites with multilayer C/SiC coating^.'.^ For SiC/SiC composites with BN interphases, if the debonding and sliding layer was between the BN and the matrix. a similar benefit proposed for the multilayer approach could be achieved. Oxidation of the BN would occur from the “outside” of the BN inwards toward the fiber. The resulting boria oxidation product would react with the Sic matrix to eventually form a borosilicate glass that would act as a “sealant” slowing diffusion of oxidizing species to the BN. In order for the fibers to be fused together or to the matrix, oxidation of the entire thickness of the BN would have to occur (Fig. l(b)). This may take a considerable amount of time considering the effects of sealing and the reduced surface area of BN exposed to oxidizing species when compared with the typical “inside” debonding case (Figs. I(a) and (b)). Therefore, the major benefit expected from an outside-debonded interphase in SiC/SiC composites would be improved intermediate-temperature mechan￾ical properties, e.g., stress-rupture, in oxidizing environments. Such behavior has been demonstrated and will be described and discussed in this work. 1 (a)). II. Experimental Procedure Sic-fiber-reinforced melt-infiltrated SiC-matrix composite pan￾els that exhibited outside debonding were fabricated from 2D￾woven, balanced, 5 harness satin, 0/90 fabric, by General Electric 104