Creep strength of magnesium-based alloys

The high-temperature creep resistance of magnesium alloys was discussed, with special reference to Mg-Al and Mg-Y alloys. Mg-Al solid-solution alloys are superior to Al-Mg solid-solution alloys in terms of creep resistance. This is attributed to the high internal stress typical of an hcp structure having only two independent basal slip systems. Although magnesium has a smaller shear modulus than aluminum, the inherent creep resistance of Mg alloys is better than that of Al alloys. The creep resistance of Mg alloys is improved substantially by the addition of Y. Solid-solution hardening is the principal mechanism of the strengthening, but the details of the mechanism have not been elucidated yet. Forest dislocation hardening in concentrated alloys and dynamic precipitation in a Mg-2.4 pct Y alloy also contribute to the strengthening. An addition of a very small amount of Zn raises the dislocation density and significantly improves the creep resistance of Mg-Y alloys. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Creep processes in magnesium alloys and their composites

A comparison is made between the creep characteristics of two squeeze-cast magnesium alloys (AZ 91 and QE 22) reinforced with 20 vol pct Al₂O₃ short fibers and the unreinforced AZ 91 and QE 22 matrix alloys. The results show the creep resistance of the reinforced materials is considerably improved by comparison with the unreinforced matrix alloys. It is suggested that creep strengthening in these short-fiber composites arises primarily from the existence of a threshold stress and the effect of load transfer. By testing samples to failure, it is demonstrated that the unreinforced and reinforced materials exhibit similar times to failure at the higher stress levels. A detailed microstructural investigation by transmission electron microscopy (TEM) reveals no substantial changes in matrix microstructure due to the presence of the reinforcement. This suggests that direct composite strengthening dominates over indirect effects. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Creep processes in magnesium alloys and their composites

A comparison is made between the creep characteristics of two squeeze-cast magnesium alloys (AZ 91 and QE 22) reinforced with 20 vol pct Al₂O₃ short fibers and the unreinforced AZ 91 and QE 22 matrix alloys. The results show the creep resistance of the reinforced materials is considerably improved by comparison with the unreinforced matrix alloys. It is suggested that creep strengthening in these short-fiber composites arises primarily from the existence of a threshold stress and the effect of load transfer. By testing samples to failure, it is demonstrated that the unreinforced and reinforced materials exhibit similar times to failure at the higher stress levels. A detailed microstructural investigation by transmission electron microscopy (TEM) reveals no substantial changes in matrix microstructure due to the presence of the reinforcement. This suggests that direct composite strengthening dominates over indirect effects. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

The effect of particle reinforcement on the creep behavior of single-phase aluminum

The effect of TiC particle reinforcement on the creep behavior of Al (99.8) and Al-1.5Mg is investigated in the temperature range of 150 °C to 250 °C. The dislocation structure developed during creep is characterized in these materials. The addition of TiC increases creep resistance in both alloys. In pure aluminum, the presence of 15 vol pct TiC leads to a factor of 400 to 40,000 increase in creep resistance. The creep strengthening observed in Al/TiC/15_p is substantially greater than the direct strengthening predicted by continuum models. Traditional methods for explaining creep strengthening in particle-reinforced materials(e.g., threshold stress, constant structure, and dislocation density) are unable to account for the increase in creep resistance. The creep hardening rate(h) is found to be 100 times higher in Al/TiC/15_p, than in unreinforced Al. When incorporated into a recovery creep model, this increase inh can explain the reduction in creep rate in Al/TiC/15_p. Particle reinforcement affects creep hardening, and thus creep rate, by altering the equilibrium dislocation substructure that forms during steady-state creep. The nonequilibrium structure generates internal stresses which lower the rate of dislocation glide. The strengthening observed by adding TiC to Al-1.5Mg is much smaller than that found in the pure aluminum materials and is consistent with the amount of strengthening predicted by continuum models. These results show that while both direct (continuum) and indirect strengthening occur in particle-reinforced aluminum alloys, the ratio of indirect to direct strengthening is strongly influenced by the operative matrix strengthening mechanisms. This article is based on a presentation made in the symposium entitled “Creep and Fatigue in Metal Matrix Composites” at the 1994 TMS/ASM Spring meeting, held February 28–March 3, 1994, in San Francisco, California, under the auspices of the Joint TMS-SMD/ASM-MSD Composite Materials Committee.     

Electron Theory Research in Mg-Y Alloy

Adding yttrium to magnesium can improve the mechanical properties, especially the mechanical behavior at high temperature. The valence electron structures of Mg-Y alloy were analyzed with the empirical electron theory of solids and molecules (EET). Calculation shows that yttrium is on the fifth hybrid level and magnesium is on the third one in pure metal crystals. By comparing with aluminum in Mg-Al alloy, it is shown that the reason why the solution strengthening effect of yttrium is better than that of aluminum in Mg-Al alloy is the enhanced bond energy according to EET. And it is concluded from EET analysis that intermetallies Mg24Y5 can significantly improve the properties of magnesium alloys because yttrium atoms oceupy the centers of the oetahedron and Mg-Y bonds efficiently strengthen the alloy matrix.     

Observations of room-temperature creep recovery in titanium alloys

Conventional α(hcp) and α(hcp)/β(bcc) titanium alloys exhibit significant primary creep strains at room temperature and at stresses well below their macroscopic yield strength. It has been previously reported in various materials systems that repeated unloading during primary creep testing may either accelerate or retard the accumulation of creep strains. These effects have been demonstrated to depend on both microstructure and the applied stress. This article demonstrates that significant room-temperature recovery occurs in technologically relevant titanium alloys. These recovery mechanisms are manifested as a dramatic increase in creep rates (by several orders of magnitude) upon the introduction of individual unloading events, ranging from 1 minute to 365 days, during primary creep tests. Significant increases in both creep rate and the total accumulated creep strain were observed in polycrystalline single α-phase Ti-6Al, polycrystalline α/β Ti-6Al-2Sn-4Zr-2Mo-0.1Si, and individual α/β colonies of Ti-6242. Based on transmission electron microscopy (TEM) studies of the active deformation mechanisms, it is proposed that the presence of significant stress concentrations within the α phase of these materials, in the form of dislocation pileups, is a prerequisite for significant room-temperature recovery. M.F. SAVAGE, formerly with the Department of Materials Science and Engineering, The Ohio State University Columbus, OH. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Nonbasal deformation modes of HCP metals and alloys: Role of dislocation source and mobility

A review is presented on the role of dislocation cores and planar faults in activating the nonbasal deformation modes, 〈c+a〉 pyramidal slip and deformation twinning, in hcp metals and alloys and in D0₁₉ intermetallic compounds. Material-specific mechanical behavior arises from a competition between altemate defect structures that determine the deformation modes. We emphasize the importance of accurate atomistic modeling of these defects, going beyond simple interatomic energy models. Recent results from both experiments and theory are summarized by discussing specific examples of Ti and Mg single crystals; Ti-, Zr-, and Mg-base alloys; and Ti₃Al ordered alloys. Remaining key issues and directions for future research are also discussed. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM and TMS committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Observations of room-temperature creep recovery in titanium alloys

Conventional α(hcp) and α(hcp)/β(bcc) titanium alloys exhibit significant primary creep strains at room temperature and at stresses well below their macroscopic yield strength. It has been previously reported in various materials systems that repeated unloading during primary creep testing may either accelerate or retard the accumulation of creep strains. These effects have been demonstrated to depend on both microstructure and the applied stress. This article demonstrates that significant room-temperature recovery occurs in technologically relevant titanium alloys. These recovery mechanisms are manifested as a dramatic increase in creep rates (by several orders of magnitude) upon the introduction of individual unloading events, ranging from 1 minute to 365 days, during primary creep tests. Significant increases in both creep rate and the total accumulated creep strain were observed in polycrystalline single α-phase Ti-6Al, polycrystalline α/β Ti-6Al-2Sn-4Zr-2Mo-0.1Si, and individual α/β colonies of Ti-6242. Based on transmission electron microscopy (TEM) studies of the active deformation mechanisms, it is proposed that the presence of significant stress concentrations within the α phase of these materials, in the form of dislocation pileups, is a prerequisite for significant room-temperature recovery. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Nonbasal deformation modes of HCP metals and alloys: Role of dislocation source and mobility

A review is presented on the role of dislocation cores and planar faults in activating the nonbasal deformation modes, <c + a> pyramidal slip and deformation twinning, in hcp metals and alloys and in D0₁₉ intermetallic compounds. Material-specific mechanical behavior arises from a competition between alternate defect structures that determine the deformation modes. We emphasize the importance of accurate atomistic modeling of these defects, going beyond simple interatomic energy models. Recent results from both experiments and theory are summarized by discussing specific examples of Ti and Mg single crystals; Ti-, Zr-, and Mg-base alloys; and Ti₃Al ordered alloys. Remaining key issues and directions for future research are also discussed. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans Louisiana, under the auspices of the following ASM and TMS committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

High-temperature deformation behavior of NiAl(Ti) solid-solution single crystals

The high-temperature deformation behavior of the solid solution-strengthened alloys Ni-47.5Al-2.5Ti and Ni-47Al-3Ti were investigated. Single crystals were deformed in compression in the “hard” 〈001〉 and “soft” 〈111〉 orientations, at temperatures between 827 °C and 1250 °C. The results show that Ti has a very powerful solute-strengthening effect in NiAl. The creep rates for the solid-solution alloys were observed to be as much as three to four orders of magnitude lower than those for unalloyed NiAl. To better understand this strong solid-solution strengthening effect, we studied the stress and temperature dependence of the creep rates for these alloys, as well as the deformation transients associated with stress changes. These results suggest that solute-drag effects dominate the creep resistance at the highest temperatures and lowest stresses. The solute-drag hypothesis is supported by calculations of the solute-size effect of Ti in NiAl and by the form of dislocation substructures found in the creep-deformed crystals. W.D. NIX is the Lee Otterson Professor of Engineering with the Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305.     

Creep deformation mechanisms in high-pressure die-cast magnesium-aluminum-base alloys

Creep of die-cast Mg alloys is described as an integral part of their plastic deformation behavior in terms of stress-strain-rate-strain relations. Creep tests yield information on yield stress, work hardening, maximum deformation resistance (minimum creep rate), and work softening. Testing in compression avoids influences by fracture. Data on the alloy AJ52 (5Al, 2Sr) in the temperature range between 135 °C and 190 °C are presented and compared to those for AZ91 and AS21. Die-cast Mg-Al alloys consist of fine grains with a grain boundary region containing intermetallic precipitates. Transmission electron microscopic observations indicate that basal glide is the dominant mechanism of deformation being supplemented by nonbasal glide and twinning to maintain compatiblity between the grains. The deformation resistance can be modeled with a composite approach assuming that the grain boundary region is relatively hard due to precipitation of intermetallic phases. The differences in long-term creep resistance at low stress are explained in terms of different strength and stability of precipitates in the different alloys. This article is based on a presentation made in the symposium entitled “Phase Transformations and Deformation in Magnesium Alloys,” which occurred during the Spring TMS meeting, March 14–17, 2004, in Charlotte, NC, under the auspices of the ASM-MSCTS Phase Transformations Committee.     

First-principles investigation of perfect and diffuse antiphase boundaries in HCP-based Ti-Al alloys

First-principles thermodynamic models based on the cluster expansion formalism, Monte Carlo simulations, and quantum-mechanical total energy calculations are employed to compute short-range-order (SRO) parameters and diffuse-antiphase-boundary energies in hcp-based α-Ti-Al alloys. Our calculations unambiguously reveal a substantial amount of SRO is present in α-Ti-6 Al and that, at typical processing temperatures and concentrations, the diffuse antiphase boundaries (DAPB) energies associated with a single dislocation slip can reach 25 mJ/m². We find very little anisotropy between the energies of DAPBs lying in the basal and prism planes. Perfect antiphase boundaries in DO₁₉-ordered Ti₃Al are also investigated and their interfacial energies, interfacial stresses, and local displacements are calculated from first principles through direct supercell calculations. Our results are discussed in light of mechanical property measurements and deformation microstructure studies in α-Ti-Al alloys. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

First-principles investigation of perfect and diffuse antiphase boundaries in HCP-based Ti-Al alloys

First-principles thermodynamic models based on the cluster expansion formalism, Monte Carlo simulations, and quantum-mechanical total energy calculations are employed to compute short-range-order (SRO) parameters and diffuse-antiphase-boundary energies in hcp-based α-Ti-Al alloys. Our calculations unambiguously reveal a substantial amount of SRO is present in α-Ti-6 Al and that, at typical processing temperatures and concentrations, the diffuse antiphase boundaries (DAPB) energies associated with a single dislocation slip can reach 25 mJ/m². We find very little anisotropy between the energies of DAPBs lying in the basal and prism planes. Perfect antiphase boundaries in DO₁₉-ordered Ti₃Al are also investigated and their interfacial energies, interfacial stresses, and local displacements are calculated from first principles through direct supercell calculations. Our results are discussed in light of mechanical property measurements and deformation microstructure studies in α-Ti-Al alloys. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Transmission electron microscopy investigation of 〈c+a〉 dislocations in Mg and α-solid solution Mg-Li alloys

The ductility of Mg alloys is limited due to a shortage of independent slip systems. In particular, c-axis compression cannot be accommodated by any of the easy slip or twinning modes. Basal-textured samples of pure Mg and Mg-15 at. pct Li were examined for the presence of 〈c+a〉 dislocations by post-mortem transmission electron microscopy (TEM) after a small deformation, which forced the majority of grains to compress nearly parallel to their c-axes. A higher density and more uniform distribution of 〈c+a〉 dislocations is found in the Li-containing alloy. Because the 1/3〈11 3〉 {11 } pyramidal slip mode offers five independent slip systems, it provides a satisfying explanation for the enhanced ductility of α-solid solution Mg-Li alloys as compared to pure Mg. The issue of 〈c+a〉 dislocation dissociation and decomposition remains open from an experimental point of view. Theoretically, the most feasible configuration is a collinear dissociation into two 1/2〈c+a〉 partial dislocations, with an intervening stacking fault on the glide plane. It is speculated that Li additions may lower the fault’s energy and, thereby, increase the stability of this glissile configuration. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Intergranular stresses in ZIRCALOY-2

The development of the understanding of the intergranular stresses in ZIRCALOY-2 is reviewed. Neutron diffraction measurements of the intergranular strains were made on rod-textured material and highly textured plate. The elastoplastic self-consistent (EPSC) model provides a sound theoretical foundation for our understanding of the behavior. The strain response of ZIRCALOY-2 to applied tensile stress is well described for two very different textures with the same slip and hardening parameters. It is almost certain that tensile twinning is the explanation for the response to compressive stress and rolling that is, as yet, incompletely understood. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Intergranular stresses in ZIRCALOY-2

The development of the understanding of the intergranular stresses in ZIRCALOY-2 is reviewed. Neutron diffraction measurements of the intergranular strains were made on rod-textured material and highly textured plate. The elastoplastic self-consistent (EPSC) model provides a sound theoretical foundation for our understanding of the behavior. The strain response of ZIRCALOY-2 to applied tensile stress is well described for two very different textures with the same slip and hardening parameters. It is almost certain that tensile twinning is the explanation for the response to compressive stress and rolling that is, as yet, incompletely understood. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Precipitation strengthening in K5-series γ-TiAl alloyed with silicon and carbon

Interstitial additions and precipitation hardening in fully lamellar gamma TiAl have been investigated in recent years, with a prime objective of improving the high-temperature creep resistance. As a result of this alloy development effort, the alloy system K5 (Ti46Al-2Cr-3Nb-0.2W) was found to show remarkably improved creep resistance when reinforced with C or C+Si additions and then aged appropriately. Precipitation strengthening is the proposed mechanism accounting for the observed creep strengthening of K5SC alloys, with emphasis being paid on the effect of B2 particles, ζ-type silicides, and H-type carbide precipitates delineating γ/γ interfaces. In this study, the creep-deformed microstructures of fully lamellar K5 (S-C)-type alloys in aged and unaged conditions were characterized using detailed electron microscopy, involving high-resolution imaging techniques and in-situ heating studies. Overall, the presence of these particles and their relative distribution result in strengthening of the lamellar structure. The particular effect of each type of precipitate (silicides vs carbides) on creep has been assessed. New information about the nature of the light-element precipitation processes has been obtained by studying the nucleation and growth of the carbide and silicide precipitates at the expense of dissolving α ₂ laths during aging. This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint Committee on Mechanical Behavior of Materials.     

Equal-channel angular extrusion of beryllium

The equal-channel angular extrusion (ECAE) technique has been applied to a powder metallurgy (P/M) source Be alloy. Extrusions have been successfully completed on Ni-canned billets of Be at approximately 425 °C. No cracking was observed in the billets, and significant grain refinement was achieved. In this article, microstructural features and dislocation structures are discussed for a single-pass extrusion, including evidence of 〈c〉 and 〈c+a〉 dislocations. Significant crystallographic texture developed during ECAE, which is discussed in terms of this unique deformation processing technique and the underlying physical processes which sustain the deformation. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

An accelerated methodology for the evaluation of critical properties in polyphase alloys

A system for more rapidly determining the strength and stiffness of polyphase alloys is presented that is based on a digital representation of the material structure. Working in concert with the representation are a number of digital tools and probes that are analogues of testing equipment and instrumentation of traditional laboratory methods. These are combined with nontraditional mechanical testing methods to complete the system. An example of an Fe-Cu system is used to illustrate the methodology. This article is based on a presentation made in the symposium entitled “Three Dimensional Materials Science” during the 2003 MS&T ’03: Materials Science & Technology Conference 2003 in Chicago, Illinois, on November 11 & 12, 2003, under the auspices of the ASM/MSCTS: Materials Science Critical Technology Sector Committee and the TMS/SMD: Structural Materials Division Committee.     

Transmission electron microscopy investigation of < c + a > dislocations in Mg and α-solid solution Mg-Li alloys

The ductility of Mg alloys is limited due to a shortage of independent slip systems. In particular, c-axis compression cannot be accomodated by any of the easy slip or twinning modes. Basaltextured samples of pure Mg and Mg-15 at. pct Li were examined for the presence of <c+a> dislocations by post-mortem transmission electron microscopy (TEM) after a small deformation, which forced the majority of grains to compress nearly parallel to their c-axes. A higher density and more uniform distribution of <c+a> dislocations is found in the Li-containing alloy. Because the pyramidal slip mode coffers five independent slip systems, it provides a satisfying explanation for the enhanced ductility of α-solid solution Mg-Li alloys as compared to pure Mg. The issue of <c+a> dislocation dissocation and decomposition remains open from an experimental point of view. Theoretically, the most feasible configuration is a collinear dissociation into two 1/2 <c+a> partial dislocations, with an intervening stacking fault on the glide plane. It is speculated that Li additions may lower the fault’s energy and, thereby, increase the stability of this glissile configuration. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committe, Joint Nuclear Materials Committee, and Titanium Committee.