Recent studies have shown that a suitably thermomechanically processed Al–Zn–Mg–Cu–Zr–Sc alloy having an essentially unrecrystallized grain structure may be subjected to superplastic deformation at a ...temperature and strain rate combination of 475
°C, 1.9
×
10
−2
s
−1 to obtain a total elongation of 650%. The present work demonstrates that the utilization of two-step strain rate at 425
°C during superplastic deformation of a similarly thermomechanically processed alloy increases the total elongation value to as high as 916%. The beneficial effect of two-step strain rate could further be realized at 350
°C to obtain a total elongation of 438%. Using electron backscattered diffraction, the present work provides a systematic assessment of the changes in (i) percentage recrystallization and (ii) recrystallized grain size with percentage elongation in the material superplastically deformed using both one- and two-step strain rates.
Recrystallized commercial purity aluminum samples were deformed to true strains of 0.095 and 0.262 by uniaxial tension. Microtexture data were analyzed to quantify orientation gradients between the ...grain interior and the grain boundary of nearest neighbor crystallites. The gradients were characterized in terms of the length over which a significant gradient was observed and the maximum misorientation. Estimated length ratios were observed to obey an inverse power law relationship with Taylor factor(s).
AA5052 was subjected to severe plastic deformation using the equal channel angular pressing (ECAP) technique. The microstructure, quantified using electron backscattered diffraction, showed that ECAP ...refined the grain size, increased the fraction of high angle boundaries (from 0.46 to 0.75) and increased total boundary area per unit volume of AA5052. ECAP increased the flow stress from about 325 to 425MPa and strain rate sensitivity from 0.005 to 0.012 and reduced strain hardening exponent from 0.34 to 0.25. Shear localization in the ECAP as well as unpressed AA5052 was studied using hat-shaped samples deformed at both quasi-static strain rates in a screw-driven machine and dynamic strain rates in a split-Hopkinson bar. The shear band formation in the hat-shaped sample was narrow and well defined for the ECAP condition as compared to the unpressed condition where the shear band was broad and diffuse, implying an increased propensity for shear localization as compared to the unpressed condition. The microstructure within the shear band of the ECAP condition sample showed that the boundary area per unit volume decreased as compared to that away from the shear band.
▶ Transformation texture of (1
1
−2
0)//ND type forms in prior-cold rolled Ti alloy. ▶ Texture strength increases with cooling rate, due to variant selection. ▶ Common α variants at grain boundary ...are preferential selected in slow cooling. ▶ Pole intensity distribution function, for a standard distribution in ODF obtained. ▶ Transformation texture under ‘strong’ and ‘no’ variant selection modeled.
The evolution of texture in a cold rolled Ti–5Ta–1.8Nb alloy sheet, during the α
→
β
→
α transformation has been studied using EBSD and XRD techniques, for different cooling rates. The sheet exhibited a basal plane type texture upon cold rolling, and a sharp ‘{1
1
−2
0}||rolling plane’ transformation texture was inherited after the heat treatment. The microtexture analysis of the lamellar α/β structure, suggested that this transformation texture arises from the {1
1
1}〈1
1
0〉 type of high temperature β texture, obeying the Burgers orientation relationship. The strength of the transformation texture was found to sharply increase with decrease in cooling rates, denoting variant selection. Two types of parent β orientations with 1
1
0 parallel to either rolling directions are possible, and among their α product variants, 3 of them are common, and can be preferentially formed at the prior-β grain boundaries. The role of grain boundary-α in influencing variant selection and the transformation texture for different cooling rates is described in this paper.
•Microstructural development during laser cladding has been studied.•In this multi component system Cr7C3 is found to be the stable carbide phase.•Phases were identified by EBSD since XRD results ...were not conclusive.•Increase in laser power and/or scanning speed reduced the carbide content.•Hardness seems to depend on phase content as well as microstructure.
Microstructural development in laser clad layers of Chromium carbide (CrxCy)-NiCrMoNb on SA 516 steel has been investigated. Although the starting powder contained both Cr3C2 and Cr7C3, the clad layers showed only the presence of Cr7C3. Microtexture measurements by electron back scattered diffraction (EBSD) revealed primary dendritic Cr7C3 with Ni rich FCC metallic phase being present in the interdendritic spaces. Further annealing of the laser clad layers and furnace melting of the starting powder confirmed that Cr7C3 is the primary as well as stable carbide phase in this multi component system. Increase in laser power and scanning speed progressively reduced carbide content in the laser clad layers. Increased scanning speed, which enhances the cooling rate, also led to reduction in the secondary arm spacing (λ2) of the Cr7C3 dendrites. The clad layer hardness increased with carbide content and with decreased dendrite arm spacing.
A super duplex stainless steel was subjected to solution annealing at 1323 K. This led to grain coarsening, ‘limited’ (~ 7 pct by area) austenite-to-ferrite phase transformation and changes in ...phase-specific chemistry. No changes in the phase boundary nature or galvanic coupling between phases were, however, noted. The general corrosion behavior was determined by the electrochemical performance of the individual phases. The corrosion performance of the ferrite phase degraded monotonically with annealing time. This was related to a combined effect of grain coarsening and dilution in alloying (chromium and molybdenum content) elements. Corrosion of the austenite phase was, however, non-monotonic: as the effects of grain coarsening was counter-balanced, at least during the initial stages of annealing, by relative molybdenum enrichment. This study thus provided clear experimental data relating phase-specific corrosion performance with annealing induced changes in grain size and local chemistry in a super duplex stainless steel.
Eutectoid wire rods were subjected to controlled thermo-mechanical processing (TMP). Both increased cooling rate and applied stress during the austenite-to-pearlite decomposition produced significant ...changes in the microstructure: major increases in the pearlite’s axial alignment and minor decreases in the interlamellar spacing. The pearlite alignment was correlated with changes in the ferrite crystallographic texture and the state of residual stress. Microstructural engineering, improved axial alignment of pearlite, through controlled TMP gave a fourfold increase in torsional ductility. TMP of eutectoid steel thus appears to have interesting technological possibilities.
Fully recrystallized hexagonal Zirconium was subjected to controlled hot compression tests. Deformation above 723 K showed both flow saturation, characteristic of dynamic recovery, and also the ...presence of fine equiaxed grains, indicating dynamic recrystallization (DRx). Though data from relative work hardening were inconclusive, a combination of transmission Kikuchi diffraction plus transmission electron microscopy clearly confirmed the presence of DRx grains. A separation between the deformed and the DRx grains was not possible with microtexture or nano-indentation data. Local internal friction measurements (or tan
δ
values), however, clearly distinguished the DRx grains from both statically recrystallized (SRex) and the hot deformed grains.
The serrated flow behavior of Al-Li, Al-Cu and Al-Cu-Li alloys was studied in solution-treated condition under a range of strain rates at ambient temperature. The serration behavior and the decrease ...in stress (
i.e
., the stress drop) in serrated flow curves are found to be dependent on both the magnitude of the strain rate and the nature and amounts of alloying elements present in these alloys. The underlying mechanisms behind the occurrence of serrations in these alloys are understood to be due to the interaction of solutes, both Cu and Li, with the dislocations.
Experimental forming limit curves (FLCs) were determined for two different grades of low-carbon steel: interstitial free (IF) and drawing quality (DQ). The grades had different interstitial content, ...clear differences in microstructural evolution, and differences in experimental FLCs. Microstructural evolution was generalized in terms of developments in crystallographic texture and in-grain misorientations. These were extrapolated further into dynamic values of normal anisotropy (
r
¯
) and strain hardening exponent (
n
), respectively. FLCs were simulated by finite element (FE) analysis. Simulations were conducted using constant (or initial) and dynamic material properties (namely,
r
¯
and
n
). Simulations using the dynamic variation in the material properties showed better comparison to the experimental FLCs.
