Chandan Mondal

Effects of different modes of hot cross-rolling in 7010 aluminum alloy: part II. mechanical properties anisotropy

The influence of microstructure and texture developed by different modes of hot cross-rolling on in-plane anisotropy (AIP) of yield strength, work hardening behavior, and anisotropy of Knoop hardness (KHN) yield locus has been investigated. The AIP and work hardening behavior are evaluated by tensile testing at 0 deg, 45 deg, and 90 deg to the rolling direction, while yield loci have been generated by directional KHN measurements. It has been observed that specimens especially in the peak-aged temper, in spite of having a strong, rotated Brass texture, show low AIP. The results are discussed on the basis of Schmid factor analyses in conjunction with microstructural features, namely grain morphology and precipitation effects. For the specimen having a single-component texture, the yield strength variation as a function of orientation can be rationalized by the Schmid factor analysis of a perfectly textured material behaving as a quasi-single crystal. The work hardening behavior is significantly affected by the presence of solute in the matrix and the state of precipitation rather than texture, while yield loci derived from KHN measurements reiterate the low anisotropy of the materials. Theoretic yield loci calculated from the texture data using the visco-plastic self-consistent model and Hill’s anisotropic equation are compared with that obtained experimentally.

A study on precipitation characteristics induced strength variation by nonlinear ultrasonic parameter

Nonlinear ultrasonic study has been carried out to characterize the variation in strength induced by precipitation characteristics. An age hardenable aluminum alloy has been taken as a model alloy for the present investigation. It is shown that the second order nonlinear ultrasonic (NLU) parameter scales with strength property that in turn depends on coherent to incoherent precipitation phase transition. The observed variations in NLU parameter has been explained by modifying an existing dislocation-coherent precipitate interaction model for harmonics generation in order to account for a weaker dislocation-semicoherent precipitate interaction. The model proposed can in general be applicable to all precipitation hardenable alloy systems undergoing coherent to incoherent precipitate phase transition.

Effects of different modes of hot cross-rolling in 7010 aluminum alloy: part I. evolution of microstructure and texture

The current study describes the evolution of microstructure and texture in an Al-Zn-Mg-Cu-Zr-based 7010 aluminum alloy during different modes of hot cross-rolling. Processing of materials involves three different types of cross-rolling. The development of texture in the one-step cross-rolled specimen can be described by a typical β-fiber having the maximum intensity near Copper (Cu) component. However, for the multi-step cross-rolled specimens, the as-rolled texture is mainly characterized by a strong rotated-Brass (Bs) component and a very weak rotated-cube component. Subsequent heat treatment leads to sharpening of the major texture component (i.e., rotated-Bs). Furthermore, the main texture components in all the specimens appear to be significantly rotated in a complex manner away from their ideal positions because of non-symmetric deformations in the two rolling directions. Detailed microstructural study indicates that dynamic recovery is the dominant restoration mechanism operating during the hot rolling. During subsequent heat treatment, static recovery dominates, while a combination of particle-stimulated nucleation (PSN) and strain-induced grain boundary migration (SIBM) causes partial recrystallization of the grain structure. The aforementioned restoration mechanisms play an important role in the development of texture components. The textural development in the current study could be attributed to the combined effects of (a) cross-rolling and inter-pass annealing that reduce the intensity of Cu component after each successive pass, (b) recrystallization resistance of Bs-oriented grains, (c) stability of Bs texture under cross-rolling, and (d) Zener pinning by Al3Zr dispersoids.

Effects of Heat Treatment on the Tensile Properties of Flow-Formed AA6082 Aluminum Alloy Tube

The present study reports the effect of the heat treatment on the tensile properties of the reverse flow-formed AA6082 Aluminum alloy tube. Tensile specimens obtained after each forming pass have been subjected to three different heat-treatment conditions viz., as-flow formed (AFF), as-flow formed followed by artificial aging (170°C/6h) and HT (solutionizing + 170°C/6h) treatments. Characterization of the tensile properties reveals that as-flow formed condition (followed by natural aging) gives the best combination of yield strength, UTS and percentage of elongation. The variations in tensile properties are correlated with microstructure of the materials.

Characterization of microstructural changes due to prolonged thermal exposure of directionally solidified Ni-base super alloy CM 247LC using ultrasonic

HighlightsCharacterized the precipitate coarsening process in Ni‐base super alloy using ultrasonic techniques.Dislocation vibration model has been used to explain the variation in the second order nonlinear ultrasonic parameter.A new microstructural parameter has been identified that varies in a similar way as ultrasonic parameters.Findings are technologically useful for life assessment of safety critical components. ABSTRACT The high temperature strength of directionally solidified Ni‐base super alloy CM 247LC strongly depends on the morphology, volume fraction, size and size distribution of &ggr;′ precipitate (Ni3Al) in the FCC &ggr; matrix. The microstructure of the alloy is engineered to achieve the right combination of these parameters that provides the required high temperature strength and creep resistance. The alloy contains high volume fraction of coherent &ggr;′ precipitates having near cubic shape. High temperature exposure of gas turbine components made out of the alloy leads to coarsening of the &ggr;′ precipitates and broadening of the &ggr; matrix channel. This in turn, adversely affects the high temperature mechanical properties of the alloy. The present study endeavours to non‐destructively characterize such detrimental changes in the microstructure that controls the mechanical properties and limits the life of components. The microstructural changes of the fully heat treated alloy exposed at 980 °C for different hours (100–1200) of thermal exposure have been characterized using ultrasonic methods. Changes in microstructural parameters due to different hours of thermal exposure have been correlated with changes in ultrasonic velocity, ultrasonic attenuation coefficient and second order acoustic nonlinearity parameter. It is observed that the change in attenuation is predominantly by absorption of the ultrasonic wave due to dislocation damping in the &ggr; channels. Nonlinear ultrasonic parameter changes with thermal exposure predominantly due to the alteration of dislocation precipitate interaction. A dislocation precipitation interaction model for ultrasonic wave distortion has been used to explain the observed variation in nonlinear parameter. A microstructural parameter has been identified that varies in a similar way as ultrasonic attenuation and second order ultrasonic parameter. It is shown that variations in the acoustic non‐linearity parameter follow the trend more closely with the identified microstructural parameter.

Attainment of an exceptionally high strength in low-carbon steel along with modest ductility through a novel heat treatment route

ABSTRACT Over the last few decades, the use of steel (the most significant structural engineering material) is facing a significant challenge due to its replacement by other materials (such as composites) possessing higher strength-to-weight ratio/specific strength. This necessitates further enhancement in the strength of steel. In particular, low-carbon steel, in the annealed condition, suffers from inherent problems of poor strength and discontinuous yielding. In this research work a novel heat treatment route of incomplete austenitisation-based cyclic ice-brine quenching has been adopted on low-carbon steel (AISI 1010 steel containing 0.1 wt.% C) without considering any costly alloying or thermo-mechanical treatment. Accordingly, exceptionally high strength (UTS = 1.7 GPa) and specific strength (226 MPa g−1cm3) are achieved after three cycles along with a modest ductility (% Elongation = 9). This is the highest strength reported so far for low-carbon steel containing 0.1 wt.% C. Yield point phenomenon is also eliminated. This is attributed to a novel microstructure consisting of highly sub-structured fine plate martensite crystals containing internal twin and dislocation tangles along with dispersion of nano-sized cementite particles and clusters of cementite particles.

Effect of Modes of Rolling on Mechanical Properties, Texture and Ballistic Performance of Al-7017 Alloy

This study describes the influence of texture and associated mechanical properties on ballistic performance of Aluminium-7017 alloy in two different (unidirectional and clock) hot rolling conditions. The change in texture has been explained in terms of β fiber in hot rolled and T6 tempered condition. A marginal variation in strength and hardness is observed with changing the mode of rolling, whereas Charpy impact values are found to be varying considerably. Results show that the unidirectional rolled material exhibits improved ballistic performance than that of the clock rolled plate. This has been attributed to different textures present in both the plates.

Thermal and Mechanical Stability of the Single Component Rotated Brass Texture in a 7010 Aluminum Alloy

The stability of a unique single, rotated Brass-{110}á556ñ component developed in a Al-Zn-Mg-Cu based 7010 alloy, during long term thermal annealing and cold rolling deformation has been systematically investigated. It is observed that this component remains stable during annealing at 465 °C over the period of 96 hrs and up to a uniaxial cold rolling reduction of 60%. The thermal and mechanical stability of the single component texture is discussed in terms of preferential growth advantage of recrystallized grains and confinement of slip activity in two major slip systems, respectively.

Effect of Roll Diameter and Modes of Rolling on Evolution of Texture in High Purity Aluminum

Present work describes the development of texture in high purity aluminum under different modes of deformation by rolling using two different roll diameters, namely 300 and 610 mm. It has been observed that the change in both the roll diameter as well as the modes of rolling has a marked influence on the evolution of texture as well as the characteristics of a- and β-fibres. The results are discussed in terms of the effects of roll gap geometry and the relevant stress conditions that affect the strain path of crystallite rotation.

Mechanical Property Anisotropy of 7010 Aluminum Alloy Sheet Having Single Rotated-Brass Texture

Mechanical property anisotropy in terms of in-plane anisotropy (AIP) of yield strength, and work hardening behavior of a heat treated 7010 aluminum alloy sheet has been investigated. The specimens were given two different types of heat treatments that result in a unique single rotated Brass-{110}á556ñ component with different texture intensity and volume fraction of recrystallization. It has been observed that the AIP increases with increase in texture intensity and volume fraction of recrystallization. The results are discussed on the basis of Schmid factor analyses in conjunction with microstructural features namely, grain morphology and precipitation. On the other hand, work hardening behavior appears to be significantly affected by the microstructural features rather than type of texture present in the samples.