V. V. Satya Prasad

Dynamic embrittlement in an age-hardenable copper-chromium alloy

Copper containing up to {approximately}1 weight % chromium is a precipitation hardening alloy exhibiting good room temperature strength, ductility and high electrical and thermal conductivity. Age-hardenable Cu-Cr alloys have been found to suffer from embrittlement in the temperature range 400--800 K. Grain boundary segregation of sulfur has been suggested to be the cause. Minor additions of Zr and Ti have been found to significantly improve the hot ductility of these alloys and this has been attributed to scavenging of grain boundary sulfur as zirconium sulfide. The mechanism of embrittlement during hot deformation processing of Cu-Cr alloy and other copper-based alloys is far from understood and efforts are continuing to understand the embrittlement process in these alloys.

PRODUCTION OF Cu–Cr ALLOYS BY IN SITU REDUCTION OF CHROMIUM OXIDE DURING ELECTRO SLAG CRUCIBLE MELTING (ESCM)

An electro slag crucible melting process for production of copper–chromium alloys is described. The process uses fine copper scrap as a raw material. After the copper scrap is melted, chromium is alloyed with copper by direct reduction of chromium oxide added to the slag. Carbon and aluminum can be used as reductants and the reduction is carried out in situ in the molten slag. Copper chromium ingots containing up to ∼1 wt % chromium were produced by this process. The process serves the dual purpose of recycling copper scrap and alloying remelted copper by chromium. This is the first time that direct reduction has been employed during an electro slag melting process. The in situ reduction technique described has the potential of being a production route for a variety of alloys. It is particularly suitable for production of difficult-to-melt alloys such as copper–chromium.

Microstructure and Mechanical Properties of Electroslag Strip and Explosively Clad Low Alloy Steel: Stainless Steel Joints

The surface properties such as wear, corrosion, oxidation resistance etc., can be improved by using suitable cladding technique. The most commonly used cladding material is stainless steel for cladding on carbon and low alloy steel base materials. Mechanical properties are considered important for satisfactory performance of clad joints used in several defence applications. In this work, cladding of a high strength low alloy steel with stainless steel was carried out using explosive cladding and electroslag strip cladding processes. The relationship between mechanical properties and microstructure of clad materials was evaluated. The bond interface in explosively clad material shows a wavy interface compared to strip clad interface. Electron probe microanalysis revealed that inter-diffusion of elements was significant in strip clad joints and insignificant in explosively clad joints. Shear strength, notch tensile strength and impact toughness of explosive clad joints are much superior compared to those in strip clad joints.

Electroslag cladding of low alloy steel with stainless steel

Abstract Cladding of a low alloy steel slab with stainless steel was carried out using a modified electroslag remelting technique. It is shown that the thickness of the cladding that can be achieved via electroslag remelting is dependent on the fill ratio used. The effect of power input on the joint profile obtained is reported. A combination of low fill ratio and relatively low power input is essential to minimise penetration of the base slab by the liquid metal. A satisfactory joint profile and defect free joint can be obtained via the optimisation of these process parameters. The clad product was successfully forged and rolled, which indicates satisfactory strength of the clad joint.

Niobium and Other High Temperature Refractory Metals for Aerospace Applications

Refractory metal alloys based on Nb, Mo, Ta, W, and Re find applications in the aerospace industries because of their high melting points and high temperature strengths. They are generally produced by powder metallurgy technique due to their very high melting points. However, when refining is desired, melting under high vacuum becomes necessary, for which nuggets or powder based electrodes are employed. Niobium is the lightest refractory metal with density close to that of nickel, and exhibits good thermal conductivity. Niobium can be alloyed to improve high temperature strength and oxidation resistance. Applications in nuclear, aerospace, and defence sectors have been reported. The goal of current research in Nb alloys is to simultaneously achieve high strength and workability, and provide protection from oxidation for long-term operation. There is strong research interest in intermetallics also. This chapter will discuss the salient features of refractory metals and alloys in general, and Nb-based alloys in particular.

Microstructure and wear behaviour of FeAl-based composites containing in-situ carbides

Iron aluminides containing carbon are promising materials for tribological applications. Because of graphite formation at higher (>20 wt%) Al-contents the addition of carbon to FeAl-based alloys has not been successful. The graphite precipitation may be avoided by addition of Zr or Ti. Dry sliding wear behaviour of FeAl-based alloys containing 1–1.5 wt% carbon with quaternary addition of Ti or Zr has been studied using ball-on-disk wear test. Effect of sliding speeds and applied loads is investigated and correlated with mechanical properties. Wear resistance of FeAl-based alloys is found to be significantly improved on addition of Ti /Zr. This is attributed to the high hardness of alloy carbides. The lower load-bearing capacity of graphite flakes in localized region was found to increase the wear rate of the alloy. The carbides such as Fe 3AlC 0.5, TiC and ZrC are embedded in the matrix after sliding wear without destruction or delamination. This significantly affects the wear resistance of FeAl-based alloys.

FeAl Based Intermetallic Matrix Composites Through Melt Route

FeAl based composites reinforced by carbide particles have attracted much attention in the recent years. In the present study, FeAl based composites were prepared by using arc melting route in argon atmosphere. The Ti/Zr addition to FeAl based alloys containing carbon have produced in situ formation of second phase particles namely TiC/ZrC respectively. The in situ precipitated TiC/ZrC carbides were found to be thermally stable and improved the mechanical properties of FeAl. The influence of these alloy carbides on the mechanical properties of FeAl based composites were studied. The addition of Ti/Zr resulted superior strength than FeAl alloy containing carbon. The mean coefficient of thermal expansion (CTEs) of FeAl based composites were also measured. The presence of these carbides significantly affected the CTE of FeAl based composites.

Microstructure and mechanical properties of Fe–7Al based lightweight steel containing carbon

Abstract The effect of carbon on the microstructure and mechanical properties of lightweight steel based on Fe–7 wt-%Al produced by air induction melting with flux cover is investigated. The ingots were hot worked to plates and were characterised. Steel containing 0.02 wt-%C exhibited a single phase microstructure Fe–Al(α), whereas steel containing 0.5 and 1.0 wt-% carbon exhibited a two-phase microstructure containing significant amounts of Fe3AlC0.5 precipitates in Fe–Al(α) matrix. Microhardness of the matrix decreases with increasing carbon content due to depletion of aluminium from the matrix to form Fe3AlC0.5 carbides. The bulk hardness, room temperature strength increases and tensile elongation decreases with increasing carbon content. However, at 873 K the improvement in strength as well as creep properties with increasing carbon content is marginal.

Effect of Ti, W, Mn, Mo and Si on microstructure and mechanical properties of high carbon Fe–10·5 wt-%Al alloy

Abstract Effect of quaternary alloying elements Ti, W, Mn, Mo and Si on the microstructure and mechanical properties of Fe–10·5Al–0·7C (wt-%) alloy has been investigated. Six different alloys were prepared by a combination of air induction melting with flux cover and electroslag remelting (ESR). The composition of the quaternary alloying element was ∼2 wt-% and was substituted for iron. The ESR ingots were hot forged and hot rolled at 1375 K. The hot rolled alloys were characterised with respect to microstructure and mechanical properties. Alloys containing W, Mn and Si exhibited two phase microstructure of Fe3AlC0·5 precipitates in α Fe–Al matrix. Whereas alloys containing Mo and Ti exhibited three phase microstructures, the additional phase being the respective carbides. Both α Fe–Al matrix and Fe3AlC0·5 precipitates have considerable amount of solubility for W, Mn and Mo whereas Si has very high solubility in α Fe–Al matrix as compared with Fe3AlC0·5 precipitates and titanium has very low solubility in both α Fe–Al matrix and Fe3AlC0·5 precipitates. Greater improvement in room temperature tensile properties was observed by the addition of Mn as compared with the addition of W. Significant improvement in tensile and creep properties was observed by the addition of Mo. Though the addition of silicon has resulted in poor room temperature ductility, there has been remarkable improvement in high temperature strength and creep properties.

Microstructural Characterisation of Ti Containing Fe-7Al-0.35C Based Low-Density Steel

In this paper, the role of Ti on the in-situ formation of carbides and its effect on the microstructure of Fe-7Al-0.35C alloy have been investigated. Initially, Thermo-Calc software was used to predict the phases present in the alloys which were validated by experimental work. Vacuum arc remelting process was used to make an alloy pancake of 10-mm thickness, which was hot-rolled to 2-mm thickness. The alloys were characterised by X-ray diffraction, optical, scanning electron microscope and electron probe micro-analysis. The results show that all the alloys exhibit two types of TiC precipitates, which are dark cuboidal as primary and dark acicular type as secondary precipitates along with grey-coloured needle-shaped κ-carbide precipitate in α(Fe–Al) matrix. The carbon present in the alloy is partitioned between TiC and κ-carbide precipitates. Addition of Ti has also resulted in grain refinement of all the alloys.