nan Gouthama

Low cycle fatigue behavior of Ti alloy IMI 834 at room temperature

Abstract Low cycle fatigue behavior of the Ti alloy IMI 834 was studied, for a bimodal microstructure with ≈14 vol.% primary α (α p ) in the matrix of transformed β, at different total strain amplitudes (Δ e t /2) from ±0.75 to ±1.7%, at room temperature. TEM examination revealed silicide particles at the interface of secondary α platelets in the transformed β, at the boundary of α p and transformed β, and extremely fine precipitates of ordered Ti 3 Al in the matrix. Cyclic softening was observed at all the above strain amplitudes. However, the degree as well as the rate of softening increased markedly at Δ e t /2⩾1%. Cyclic softening was much less at low strain amplitude (Δ e t /2⩽0.8%). The increase in the degree and the rate of softening at higher strain amplitudes is associated with increase in the number and more complete shearing of the ordered Ti 3 Al precipitates, from increase in the number of slip bands and glide dislocations. The increase in the number of glide dislocations in each cycle, with increase in strain amplitude occurs from increase in the effective strain rate to maintain the cyclic frequency at constant level. Bi-linearity was observed in the Coffin–Manson relationship and it was found to be associated with change in the deformation behavior from low to high strain amplitude.

Alloy design of ductile phosphoric iron: Ideas from archaeometallurgy

Alloy design criteria to produce ductile phosphoric irons have been proposed based on a detailed microstructural study of ancient Indian irons. The alloy design aims at avoiding phosphorus segregation to the grain boundaries by (a) soaking the phosphoric iron at high temperatures within the ferrite + austenite region to precipitate austenite allotriomorphs, (b) utilizing a critical amount of carbon to segregate to grain boundaries, and (c) precipitation of some of the phosphorus in solid solution in the ferrite matrix as fine coherent phosphide precipitates.

Low cycle fatigue behaviour of a multiphase medium carbon microalloyed steel processed through rolling

Abstract A multiphase (ferrite–bainite–martensite) microstructure was developed in an automotive grade medium carbon microalloyed steel 38MnSiVS5 through a two-step cooling and annealing process following controlled rolling. The tensile and low cycle fatigue properties of the multiphase steel are reported and compared with those of multiphase and tempered martensite microstructures obtained by forging.

Transmission electron microscopic evidence for cavity nucleation during superplastic flow

Abstract The cavitation behavior of a quasi-single phase superplastic copper alloy was studied using transmission electron microscopy. Clear evidence for the nucleation of cavities during superplastic flow is presented. Illustrations of the conditions under which cavities nucleate during a mesoscopic grain boundary sliding event are provided.

Porous copper template from partially spark plasma-sintered Cu-Zn aggregate via dezincification

Present work deals with the preparation of spark plasma-sintered Cu-Zn aggregate (5, 10 and 20 wt% Zn) with interfacial bonding only starting from elemental powders of Cu and Zn (99.9% purity) and subsequently making of porous template of Cu by dezincification. Sintering is done so as to achieve only interfacial bonding with the aim to maintain maximum potential difference between the Cu and Zn particles during dezincification process in various solutions, viz. 1 N HCl and 3.5 wt% NaCl solutions. X-ray diffraction, optical microscopy and SEM-EDS are carried out to examine microstructural evolution and subsequent changes in hardness with sintering temperatures and different Zn percentages. Dezincification and pore formation are conducted on sintered 0.5 mm thick 12 mm diameter disc samples. The size, distribution and nature of pores in porous templates of Cu are then investigated using optical microscopy and SEM-EDS analysis.

Transmission electron microscopy studies of thermomechanically control processed multiphase medium-carbon microalloyed steel: Forged, rolled, and low-cycle fatigued microstructures

A ferrite-bainite-martensite (F-B-M) microstructure was produced in a medium-carbon microalloyed (MA) steel through two routes, namely, low-temperature finish forging and rolling, followed by a two-step cooling (TSC) and annealing. Transmission electron microscopy (TEM) was employed to study the microstructural evolution in control forged and rolled material after TSC followed by annealing (TSCA). A TEM investigation was also carried out on samples low-cycle fatigue (LCF) tested at low and high total strain amplitudes of 0.4 and 0.7 pct in case of the forged steel (F-B-M(F)TSCA) and 0.55 and 0.8 pct for the rolled steel (F-B-M(R)TSCA), respectively. Microstructural changes accompanying the LCF testing were identified. The two-step cooled microstructure processed through forging (F-B-M(F)TSC) as well as rolling (F-B-M(R)TSC) revealed a complex multiphase microstructure, along with films and blocks of retained austenite. In both microstructural conditions, vanadium carbide precipitates were too fine to be identified after the TSC treatment. Annealing after TSC produced a stress-free microstructure. The F-B-M(F)TSCA microstructure predominantly consisted of granular/lower bainite, lath martensite, and polygonal ferrite with interlath films as well as blocks of retained austenite, while the F-B-M(R)TSCA microstructure predominantly consisted of lath martensite, granular/lower bainite, and polygonal ferrite with interlath strips/films of retained austenite. Lath martensite content was higher in the F-B-M(R)TSCA condition than in the F-B-M(R)TSCA condition. In both conditions, vanadium carbide precipitates could be seen after annealing. Fatigue-tested F-B-M(F)TSCA microstructure up to a total strain amplitude of 0.4 pct and F-B-M(F)TSCA microstructure up to a total strain amplitude of 0.55 pct were stable. Lath martensite did not undergo deformation and in both microstructural conditions dislocation cell structures were not observed in the ferrite or bainite regions. The interlath retained austenite strips/films played a significant role in preventing the softening during fatigue loading. First, it was stable up to a total strain amplitude of 0.4 and 0.55 pct in the respective microstructures. Second, it underwent heavy deformation during fatigue loading at high total strain amplitudes, thereby accommodating the strain. Fatigue-tested F-B-M(F)TSCA microstructure at a total strain amplitude of 0.7 pct and F-B-M(R)TSCA microstructure at a total strain amplitude of 0.8 pct revealed deformed bainite/martensite laths, dislocation cells, and slip bands in the ferrite regions, which are characteristic features of cyclic softening. The retained austenite transformed to martensite through a strain-induced transformation mechanism and, at that stage, the microstructure contained in addition dislocation-rich bainite and ferrite.