828 Y.T.Zhu et al.Seripta Materialia 51 (2004)825-830 822…25%1里-502% 660.68Mp 6 25 Los Alamos Los Alamos Fig.2.Plate-implants for bone osteosynthesis made of nanostructured Fig.1.An ECAP-processed Ti rod,which is about 50 mm in diameter Ti. and 170 mm in length.The unit on the ruler is inch. a new material.One specific example is the use of NS 3.1.Applications driven by superior properties pure Ti for dental implants.Typical implants have diameters greater than 3 mm because the cyclic loads It is generally easier to process the lower strength associated with chewing can reach levels that push metals such as Al or Cu.Also,a more thorough conventional Ti towards the fatigue performance limit. However.the small lower front teeth can be so closely knowledge base is currently available for these metals [18].For the SPD processing of Al and Cu,special spaced that they require smaller diameter implants.By applications requiring limited-production volumes will introducing NS Ti possessing significantly higher fatigue strength,it will be possible to use 2 mm or smaller undoubtedly initiate the first applications of these materials.Later,after the economics of SPD processing diameter implants to replace the lower front teeth.For are well established,it is reasonable to assume that high- dental implants,and many other medical devices,the volume production will become attractive.Lightweight virtues of superior material properties are determined structures of Al alloys,as in weight-sensitive products not through specific materials properties requirements or testing but through the fabrication of devices from such as aircraft,bicycles,automobiles and boats,will probably appear first.Limited production demonstra- the new material and the subsequent simulated or in- tions for components manufactured in small volumes service evaluation of the performance of the device. will lead the way.One example is bicycle components. Thus it is critical to be able to fabricate manufacturing- For both mountain bikes and road racers,the added scale sizes and quantities of NS materials for evaluation strength achievable in the SPD-processed alloy equates in specific applications. directly to weight savings in the structural frame tubing The high strength of NS materials also makes them and hardware components such as the gearing,pedals, ideal for making micro-devices and this is an exciting shifters,rims and spokes.Since the cost of bicycle and rapidly developing field.For example,high strength frames purchased by enthusiasts can often exceed $3000, micro springs and gears have been made of NS Ni-Mn there is ample opportunity for incorporating high-per- alloys via electrodeposition [3]. formance materials into these specialist applications. Other early uses of SPD metals will develop for 3.2.Applications driven by superior manufacturability applications where there are strong market drivers.For example,there is a high level of competition and inno- 3.2.1.Machinability and forgability vation with advanced materials in the medical device For products that are directly machined to shape industry and this is supported by the growing societal from SPD-processed mill products,the feed rates and interest in products that extend or enhance the quality of cutting depths can be increased because of the manner in life.One example is plate-implants for bone osteosyn- which the deformation occurs under the machining thesis made of NS Ti (see Fig.2)[20].The enhanced conditions.Processing by SPD leads to a smoother fatigue performance that is possible in SPD metals is surface finish and a reduction in tool wear.For some particularly attractive for Ti and Ti alloys used for specialized products,the largest portion of the cost may prosthetics.Specific requirements for medical devices be associated with the machining.For example,the ratio are wide ranging,depending upon the impact that the of the machining cost to the material cost is greater than enhanced properties may have on the market advantage a factor of 10 for some sporting goods products,thereby that is imparted to a given product.Generally speaking, creating a significant incentive for reducing the an enhancement of greater than 25%over the properties machining cost through material substitution.In some of conventional metals is necessary to motivate adopting cases the superior surface finish from machining of the3.1. Applications driven by superior properties It is generally easier to process the lower strength metals such as Al or Cu. Also, a more thorough knowledge base is currently available for these metals [18]. For the SPD processing of Al and Cu, special applications requiring limited-production volumes will undoubtedly initiate the first applications of these materials. Later, after the economics of SPD processing are well established, it is reasonable to assume that high￾volume production will become attractive. Lightweight structures of Al alloys, as in weight-sensitive products such as aircraft, bicycles, automobiles and boats, will probably appear first. Limited production demonstra￾tions for components manufactured in small volumes will lead the way. One example is bicycle components. For both mountain bikes and road racers, the added strength achievable in the SPD-processed alloy equates directly to weight savings in the structural frame tubing and hardware components such as the gearing, pedals, shifters, rims and spokes. Since the cost of bicycle frames purchased by enthusiasts can often exceed $3000, there is ample opportunity for incorporating high-per￾formance materials into these specialist applications. Other early uses of SPD metals will develop for applications where there are strong market drivers. For example, there is a high level of competition and inno￾vation with advanced materials in the medical device industry and this is supported by the growing societal interest in products that extend or enhance the quality of life. One example is plate-implants for bone osteosyn￾thesis made of NS Ti (see Fig. 2) [20]. The enhanced fatigue performance that is possible in SPD metals is particularly attractive for Ti and Ti alloys used for prosthetics. Specific requirements for medical devices are wide ranging, depending upon the impact that the enhanced properties may have on the market advantage that is imparted to a given product. Generally speaking, an enhancement of greater than 25% over the properties of conventional metals is necessary to motivate adopting a new material. One specific example is the use of NS pure Ti for dental implants. Typical implants have diameters greater than 3 mm because the cyclic loads associated with chewing can reach levels that push conventional Ti towards the fatigue performance limit. However, the small lower front teeth can be so closely spaced that they require smaller diameter implants. By introducing NS Ti possessing significantly higher fatigue strength, it will be possible to use 2 mm or smaller diameter implants to replace the lower front teeth. For dental implants, and many other medical devices, the virtues of superior material properties are determined not through specific materials properties requirements or testing but through the fabrication of devices from the new material and the subsequent simulated or in￾service evaluation of the performance of the device. Thus it is critical to be able to fabricate manufacturing￾scale sizes and quantities of NS materials for evaluation in specific applications. The high strength of NS materials also makes them ideal for making micro-devices and this is an exciting and rapidly developing field. For example, high strength micro springs and gears have been made of NS Ni–Mn alloys via electrodeposition [3]. 3.2. Applications driven by superior manufacturability 3.2.1. Machinability and forgability For products that are directly machined to shape from SPD-processed mill products, the feed rates and cutting depths can be increased because of the manner in which the deformation occurs under the machining conditions. Processing by SPD leads to a smoother surface finish and a reduction in tool wear. For some specialized products, the largest portion of the cost may be associated with the machining. For example, the ratio of the machining cost to the material cost is greater than a factor of 10 for some sporting goods products, thereby creating a significant incentive for reducing the machining cost through material substitution. In some cases the superior surface finish from machining of the Fig. 1. An ECAP-processed Ti rod, which is about 50 mm in diameter and 170 mm in length. The unit on the ruler is inch. Fig. 2. Plate-implants for bone osteosynthesis made of nanostructured Ti. 828 Y.T. Zhu et al. / Scripta Materialia 51 (2004) 825–830