I.S. Batra

Microstructure and properties of a Cu-Cr-Zr alloy

Abstract Copper-based dilute Cu–Cr–Zr alloys and their minor modifications, because of their excellent thermal conductivity, strength and fatigue resistance, are commonly used in an aged condition in heat transfer elements. However, in comparison to dilute Cu–Cr binary alloys in which the precipitation of chromium has been studied extensively in the last two decades, attempts at delineating the morphology, composition and crystallography of precipitates in Cu–Cr–Zr alloys have been few and only partially successful. The role of zirconium has also remained largely unresolved. In the present work, the precipitation in an alloy having a nominal composition of Cu–1 wt% Cr–0.1 wt% Zr has been shown to take place through the formation of a metastable ordered fcc phase. Also, the improvement in fatigue resistance due to the addition of zirconium has been ascribed to lowering of the stacking fault energy (SFE) of the alloy.

Precipitation in a Cu-Cr-Zr alloy

Transmission electron microscopy (TEM) investigations of the early stages of precipitation of a b.c.c. phase in f.c.c. matrix have been carried out in a dilute Cu-Cr-Zr alloy. The initial product of decomposition, characterized by a state of order, which mimics a cube-on-cube orientation relationship (OR) with the matrix appears prior to ordered b.c.c. phase precipitates showing Nishiyama-Wassermann (N-W) OR.

A dilatometric study of the continuous heating transformations in 18wt.% Ni maraging steel of grade 350

Abstract Dilatometric studies in 350 grade maraging steel (M350) were carried out to study the effect of heating rate and cold rolling, on precipitation, and martensite to austenite transformation. Recrystallized and cold rolled materials were subjected to controlled heating–holding–cooling cycles, under vacuum. The martensite to austenite transformation splits into two steps at lower heating rates. The first step enhanced by slow heating rate, occurs through a diffusion process, while the second step, enhanced by a fast heating rate, occurs though a shear process. The extent of the total martensite to austenite transformation is independent of heating rate, whereas the extent of precipitation decreases with increasing heating rate. Cold rolling of maraging steel results in a dilatational anomaly, which decreases with heating rate. At a given heating rate, cold rolling does not affect the extent of precipitation although it marginally lowers the precipitation start temperature and rate.

On the sequence of clustering and ordering in a meltspun Cu–Ti alloy

Abstract Although it is well established that dilute Cu–Ti alloys with titanium in the range of 2.5–5 wt.% decompose by a spinodal mechanism, the sequence of ordering and clustering processes in the early stages has been a matter of controversy. An attempt has been made in this work to resolve some of the issues by carrying out transmission electron microscopy (TEM) investigations on a dilute meltspun Cu–Ti alloy. Decomposition was studied as a function of ageing over a temperature range of 573–723 K. The results seem to suggest that clustering precedes the formation of long range ordered (LRO) phases in this alloy. Formation of a transitory special point N 3 M phase was observed for the first time in this work. This disappeared on prolonged ageing giving rise to the metastable Cu 4 Ti (D1 a ).

Strengthening of a 12CrMoV turbine blade steel by retempering

Commercially available martensitic 12CrMo, 12CrMoV, and HCrMoVNb steels in the tempered condi-tion are often used to fabricate turbine blades. Tempering, done at the processing stage itself, is usually carried out at a temperature approximately 100 to 150 ° above the service temperature. At the service temperature, the steel undèrgoes a second tempering. The effect of this second tempering at a lower tem-perature on the strength of 12CrMoV steel is delineated and discussed in this paper.