Fabrication of W-Cu functionally graded composites using high energy ball milling and spark plasma sintering for plasma facing components

W-Cu functionally graded composites (FGCs) up to six layers have been developed using high energy ball milling and spark plasma sintering (SPS) at a lower temperature of 900 °C. The relative density of W-Cu composites increased from 85.4% (W₈₀Cu₂₀ layer) to 95.7% (W₂₀Cu₈₀ layer) with increasing Cu content. All the W-Cu FGCs exhibited a graded structure even after SPS and showed a gradual change in hardness, Young’s modulus, and coefficient of thermal expansion (CTE). Furthermore, W-Cu composites showed a CTE and modulus between those of W and Cu and could be used as an intermediate layer between W and Cu in plasma facing components. The thermal cycle testing at 800 °C has confirmed that the W-Cu FGCs developed in this study can withstand thermal shock and showed a superior performance over directly bonded W-Cu sample. The W-Cu FGCs developed in the present study are not only suitable for plasma facing components but can also be used where the thermal stresses are introduced due to the large mismatch in CTE or elastic modulus.     

Application of mechano-chemical synthesis for protective coating on steel grinding media prior to ball milling of copper

One of the major sources of contamination during mechanical milling/alloying is from the surface erosion of the container and the grinding medium. This can either be prevented by using grinding medium and container of same material of the milled material or by adding a coating of the milled material on them. The paper describes the observations made during a mechano-chemical reaction, being used for coating the balls and vials in a planetary ball mill. Visual observation, XRD, optical micrography and EDS analysis were used to understand the progress of the reaction. Copper was successfully coated on the steel balls and vials. The method can easily be adopted in daily production purposes, prior to mechanical milling of a Cu-based powder for prevention of Fe contamination.     

Numerical and experimental investigations on the residual stresses of the butt-welded joints

Welding is a reliable and efficient joining process in which the coalescence of metals is achieved by fusion. Localized heating during welding, followed by rapid cooling, can generate residual stresses in the weld and in the base metal. Estimating the magnitude and distribution of welding residual stresses is important. This study applies thermal elasto-plastic analysis, using finite element techniques, to analyze the thermomechanical behavior and evaluate the residual stresses in butt-welded joints. The residual stresses at the surface of the weldments were measured by X-ray diffraction. The results of finite element analysis were compared with experimental residual stress data to confirm the accuracy of the method. The aim is to present data that may confirm the validity of currently employed fabrication processes in welded structures and even improve them.