STUDIES ON INTERMETALLICS PRODUCED BY MECHANICAL ALLOYING AND GAS REDUCTION

Abstract

The aim towards the present Master Thesis work was to study two different methods namely Mechanical Alloying and Gas Reduction towards the production of Ti-Aluminides and Cu-W intermetallics respectively. For this purpose High energy ball milling was employed to produce Nano-crystalline Ti-Al powders and a H2 gas reduction route was used in separate experiments to produce Cu-W intermetallic on the metallic Cu substrate. To produce Nano-crystalline Ti-aluminides milling was conducted in a Zirconium steel vial with steel balls using elemental powders. Aluminum (48 at %), titanium (51 at %) and graphite (coated with Ni-P)-1 at% was used and milling was conducted for 60 hours. The ball to powder weight ratio of 15:1 and rpm 100 was used. Powder samples were characterized using X-ray diffraction and scanning electron microscopy. Analysis showed that graphite acts as a binder and leads to grain refinement, and gamma phase (TiAI) has been formed but in localized regions only even after 60 hours of milling. In the other experiments a W coating on the surface of the metallic Cu surface is developed. For this purpose a hydrogen reduction route was followed to achieve the nano-sized particles on the final surface. The hydrogen reduction process was adopted after a critical survey of the earlier successful results, obtained in the laboratory of Materials Science department of KTH Sweden. Presently the surface of a sheet of metallic Cu was first oxidized and then, coated with the slurry of W03. After sintering in an inert gas (Ar) atmosphere for 2-3 hrs; the oxide coated samples were subjected to reduction using the hydrogen gas. After a preliminary investigation of the impact of various process parameters, the reduction process was standardized by conducting the reaction isothermally at 910 K for a period of 3 hrs; before they were furnace-cooled in the reductant gas atmosphere. The samples with W coating thus prepared were characterized by the SEM, XRD and Laser Microscopy techniques. The impact of process parameters on the surface of the coating obtained was examined. The experimental results showed the formation of nano sized Cu/W intermetallic in the coated surface and the thickness of the coating was confined within the range of 30 gm. the hydrogen reduction method was thus found to offer a novel process route towards achieving coatings of alloy on metallic substrate.