Gregory Henshall

Bio: Gregory Henshall is an academic researcher from Hewlett-Packard. The author has contributed to research in topics: Deformation (engineering) & Creep. The author has an hindex of 6, co-authored 16 publications receiving 119 citations. Previous affiliations of Gregory Henshall include University of Texas at Austin.

Warm-temperature tensile ductility in Al-Mg alloys

Abstract: Several binary and ternary Al alloys containing from 2.8 to 5.5 wt pct Mg were tested in tension at elevated temperatures (200°C to 500°C) over a range of strain rates (10−4 to 2.0 s−1). Tensile ductilities of up to 325 pct were obtained in binary Al−Mg alloys with coarse grains deformed in the solute-drag creep regime. Under test conditions in which solute-drag creep controls deformation, Mg in concentrations from 2.8 to 5.5 wt pct neither affects tensile ductility nor influences strain-rate sensitivity or flow stress significantly. Strength is shown to increase with increasing Mg concentration, however, in the power-law-break down regime. The solute-drag creep process, which leads to superplastic-like elongations, is shown to have no observable grain-size dependence in a binary Al−Mg material. Ternary alloying additions of Mn and Zr are shown to decrease the strain-rate sensitivity during solute-drag creep, negatively influencing ductility. An important cause of reduced ductility in the ternary alloys during creep deformation is found to be a transition from necking-controlled failure in the binary alloys to cavitation-controlled failure in the ternary alloys investigated. An increase in ternary element concentration, which can increase the relative volume percentage of proeutectic products, increases cavitation.

Ductile-phase toughening in V-V3Si in situ composites

Abstract: This article describes the room-temperature fracture behavior of ductile-phase-toughened V-V3Si in situ composites that were produced by arc melting (AM), cold-crucible induction melting (IM), and cold-crucible directional solidification (DS). Composites were produced containing a wide range of microstructures, interstitial impurity contents, and volume fractions of the ductile V-Si solid solution phase, denoted (V). The fracture toughness of these composites generally increases as the volume fraction of (V) increases, but is strongly influenced by the microstructure, the mechanical properties of the component phases, and the crystallographic orientation of the (V) phase with respect to the maximum principal stress direction. For eutectic composites that have a (V) volume fraction of about 50 pct, the fracture toughness increases with decreasing “effective” interstitial impurity concentration, [I]=[N]+1.33 [O]+9 [H]. As [I] decreases from 1400 ppm (AM) to 400 ppm (IM), the fracture toughness of the eutectic composites increases from 10 to 20 MPa √m. Further, the fracture toughness of the DS eutectic composites is greater when the crack propagation direction is perpendicular, rather than parallel, to the composite growth direction. These results are discussed in light of conventional ductile-phase bridging theories, which alone cannot fully explain the fracture toughness of V-Si in situ composites.

Enhanced tensile ductility of coarse-grain Al-Mg alloys

Abstract: The development of methods for obtaining high tensile elongation in aluminum alloys is of great importance for the practical forming of near-net-shape parts. Current superplastic alloys are limited in use by high material costs. The utilization of solute-drag creep processes, the approach used in this study, to obtain enhanced tensile ductility in aluminum alloys has lead to tensile elongations of up to 325% in simple, binary Al-Mg alloys with coarse grain sizes. This method has the advantage of lowering processing costs in comparison with superplastic alloys because a fine grain size is not necessary. Whereas superplastic alloys typically have a strain-rate sensitivity of m = 0.5, the enhanced ductility Al-Mg alloys typically exhibit m = 0.3 where maximum ductility is observed. Although a strain-rate sensitivity of rn = 0.5 can lead to elongations of over 1000% (superplastic materials) a value of m = 0.3 is shown experimentally to be sufficient for obtaining elongations of 150% to a maximum observed of 325%. Enhanced ductility is also affected strongly by ternary alloying additions, such as Mn, for which a preliminary understanding is pursued.

Addressing opportunities and risks of pb-free solder alloy alternatives

Abstract: Significant innovations in Pb-free solder alloy compositions are being driven by volume manufacturing and field experiences. As a result, the industry has seen an increase in the number of Pb-free solder alloy choices beyond the common near-eutectic Sn-Ag-Cu (SAC) alloys. The increasing number of Pb-free alloys provides opportunities to address shortcomings of near-eutectic SAC, such as the poor mechanical shock performance, alloy cost, copper dissolution, and poor mechanical behavior of joints in bending. At the same time, the increase in alloy choice presents challenges in managing the supply chain and introduces a variety of technical and logistical risks, such as a potential decrease in thermal fatigue resistance and the complexity of managing process parameters given the variability of alloy compositions. This paper summarizes the results of an iNEMI project to address the opportunities and risks of new Pb-free alloy alternatives. The results of our analysis of the state of industry knowledge on Sn-Ag-Cu alloy alternatives are provided, and focus areas for closing key gaps are identified. Progress in updating or creating industry standards to manage the introduction and use of new alloys is also presented. Finally, our plans to investigate thermal fatigue reliability of new alloys are described.

Dislocation creep behavior in Mg–Al–Zn alloys

Abstract: The climb-controlled dislocation creep behavior was investigated in Mg–Al–Zn alloys of AZ31, AZ61 and AZ91 with different aluminum contents. The flow stress increased with the increase of aluminum content under the same deformation conditions. At high temperatures, the stress exponent was 5 and the activation energy was close to that for lattice diffusion of magnesium, whereas at low temperatures the stress exponent was 7 and activation energy was close to that for pipe diffusion for all alloys. By incorporating the effective diffusion coefficient and stacking fault energy into a constitutive equation, the dislocation creep behavior of magnesium alloys can be described by a single relation.