Hardening (metallurgy)

About: Hardening (metallurgy) is a research topic. Over the lifetime, 25584 publications have been published within this topic receiving 376012 citations.

Cyclic deformation behavior of single crystal NiTi

Abstract: Single crystals of NiTi (with 50.8 at.% Ni) were subjected to cyclic loading conditions at room temperature which is above the M s (martensite start) temperature of −30°C. The single crystals exhibited remarkable cyclic hardening under zero to compression strain control experiments. The stress range under strain control increased by as much as a factor of 3 in compression. The increase in stress range is primarily due to the increasing strain hardening modulus. In the tension case, loop shape changes occurred but the increase in stress range is rather small. The fatigue cycling was undertaken with a strain range of 3% which is far below the theoretical transformation strains levels exceeding 6%. The maximum stress levels reached in the experiments are below those that cause martensite slip. Therefore, the stress–strain response is governed by transformation from the austenite to the martensitic phases and the dislocation structure evolution in the austenite domains. Two single crystal orientations [148] and [112] were examined during the experiments with single and double CVP (correspondent variant pair) formations respectively. The strain hardening in compression cases is rather substantial with the stress range in the double CVP case surpassing the single CVP case. Two heat treatments were selected to produce coherent and incoherent precipitates in the microstructure respectively. The influence of the coherent precipitates on the stress–strain response is significant as they lower the transformation stress from austenite to martensite, and at the same time, they raise the flow stress of the austenite and martensite domains leading to higher saturation stresses in fatigue.

Prismatic slip in α-titanium single crystals

Abstract: Single crystals of Ti, oriented favorably for prismatic slip and containing two levels of interstitial impurities, have been deformed in tension at temperatures between 78 to 1120 K. The stress-strain curves exhibit three stages of hardening similar to those of Zr and of fcc crystals. The work hardening rate in Stage II, θII/G is lower in Ti than in Zr. From the strain rate dependence of the stress at the onset of Stage III, the stacking fault energy on the prism planes of Ti has been estimated as 0.145 Joules/m2. The relative values of stacking fault energy for Ti and Zr are consistent with a dissociation model which is based on the hcp ai bcc transformation. The thermally activated prismatic slip below 250 K is controlled by the interaction of dislocations with interstitial solute atoms. Above 250 K the dislocation mechanism for plastic flow is not clearly understood.

Phase chemistry and precipitation reactions in maraging steels: Part I. Introduction and study of Co–containing C–300 steel

Abstract: This article introduces a series of studies of phase transformations in maraging steels. Atom-probe field-ion microscopy (APFIM) was the main research technique employed. Hardness measurements, transmission electron microscopy (TEM), and thermochemical calculations were also used. The composition and morphology of precipitates in the commercial-grade C-300 steel were compared for different aging times at 510 °C to investigate the aging sequence. Both Ni3Ti and Fe7Mo6 were found to contribute to age hardening. The decomposition starts with the formation of small Mo-enriched Ni3Ti particles at very short aging times. The Fe7Mo6 phase forms at a later stage of aging. The matrix concentrations of both Ti and Mo were measured and were found to be low after standard aging conditions. The observation of the Fe7Mo6 μ phase is supported by thermochemical calculations. Austenite reversion has been found at the aging temperature, and its composition approaches the predicted equilibrium composition after 8 hours of aging.

Research on aging precipitation in a Cu–Cr–Zr–Mg alloy

Abstract: The effects of aging processes on the properties and microstructure of Cu–0.3Cr–0.15Zr–0.05Mg lead frame alloy were investigated. Aging precipitation phase was dealt with by transmission electronic microscope (TEM). After solid solution was treated at 920 °C and aged at 470 °C for 4 h, the fine precipitation of an ordered compound CrCu 2 (Zr, Mg) is found in copper matrix as well as fine Cr and Cu 4 Zr. Along the grain boundary, there are larger chromium. The hardness and electrical conductivity can reach 109 HV and 80% IACS, respectively. Sixty percent cold-rolled deformation prior to aging at 470 °C enhances the hardness of the alloy. The coherent precipitates Cr in copper matrix and the dislocations pinned by the fine precipitates are responsible for maximum strengthening of the alloy. So the hardness 165 HV and electrical conductivity 79.2% IACS are available.