Papers by Keyword: Physical Metallurgy

Abstract: Significant advantages in weight reduction and increased strength have place advanced aluminum-lithium alloys at forefront of aerospace materials research. These alloys are being developed to fulfill the ever increasing need for high strength, high properties, light weight and cost effective for aerospace industry. Conventional aluminum alloys has long been in service for aerospace application. The addition of lithium to aluminum improves modulus and decrease density compared to conventional aluminum alloys. Atomic weight of lithium is 7 mass units compared to aluminum 23 mass units, hence there is density reduction of about 3% for each weight percent addition of lithium and about 6% increase in Youngs modulus. In principle weight saving for aerospace structural parts could reach up to 15 %. This paper examines effect of lithium addition on properties, physical metallurgy; various phases developed during processing of these alloys. The addition of Lithium to aluminum form coherent, low density Al₃Li (δ^׳) precipitates. However the binary alloys have poor mechanical properties which are attributed to strain localization and shearing of soft Al₃Li (δ^׳) precipitates. This problem has been solved by development of ternary and quaternary alloys containing copper and magnesium. In all aluminum-lithium alloys, small addition of zirconium or scandium is done to improve recrystallization. The new developed aluminum lithium alloys series Al-Li-Cu-X are potential candidate to replace existing conventional alloys in terms of enhanced properties with reduced density.

Abstract: Stainless steel bar and wire products that cater to the high technology application in defence, nuclear, aerospace, oil field and chemical engineering is an area poised for rapid growth in India. The advancing capabilities of alloy steel plants in India have enabled mastering of techniques to make a wide variety of stainless steels. However, there are increasing challenges to meet the advanced property requirements, which call for a basic understanding on the structure property relationship that are influenced by appropriate alloy design and down-stream processing. The special steel industry cater to a wide variety of stainless steels namely ferritic, martensitic, austenitic and precipitation hardenable categories for meeting requirements of high technology. One of the process for making the primary stainless steels is Vacuum Oxygen Decarburisation process. For advanced applications, the primary melted steel is again secondary refined using electroslagremelting for the management of solidification structures and control of inclusions. In the austenitic grades, the hot forged and hot rolled heat treated steels, careful choice of chemistry controls the delta ferrite content and ensures uniformity of the grain size in the product during deformation processing and heat treatment. In the martensitic stainless steel grades, focus is given to delta ferrite, grain size control and appropriate tempering treatment. In the precipitation hardenable steels grades the aging reactions and hot deformation range have to be optimised for deriving specified mechanical properties. Special grades are produced using non ESR and ESR routes to meet high temperature applications such as turbine blades and bolting. In these grades control of delta ferrite content, carbides, carbo-nitrides in the matrix has a deep influence on the mechanical and sub zero fracture properties. In the ferritic stainless steel grade grain size control is critical. The presentation would bring forth the correlation between the alloy design, processing and properties that were achieved in the products mentioned above to meet some of the challenging requirements.