Effect Of Heating Rate and Sintering Temperature on Mechanical Properties of W-Cu Composites Produced via Spark Plasma Sintering
Abstract
This work was done to investigate the effect of heating rate and sintering temperature on the structure and mechanical properties of W-50Cu (wt.%) composites using spark plasma sintering technique. For investigate the effect of sintering temperature, the W-50Cu composites were sintered at temperature in the range of 900 to 975oC for 30 min using the heating rate of 50 oC/min meanwhile in order to see the effect of heating rate, the composites were sintered at 950 oC for 30 min at different heating rate from 25 to 200oC/min. The results show that all the sintered composites have a good distribution of W particles in Cu matrix. The increase of sintering temperature led to higher density, larger W average particle size and better strain at break (by compressive test), however, the hardness has a tendency to decrease at higher sintering temperature. The heating rate how an opposite effect in comparison with sintered temperature. The increase of heating rate led to the lower density, smaller W particles and lower strain at break of sintered sample but higher Vickers hardness.
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Introduction
Tungsten-copper (W-Cu) based composites have been attracted in many fields due to their high hardness and wear resistance, good electrical conductivity as well as the low coefficients of thermal expansion and good electric-erosion resistance [1, 2]. The applications of these composites are the electric and electronic materials for resistance welding electrodes, electric discharge machine, heat-sink materials and potential materials for military applications including armor-piercing, shaped charge liner and ammunition materials [1, 3-6]. Because of the large deviation in melting point between W and Cu, W-Cu based composites are fabricated by powder metallurgy technology including liquid phase sintering and infiltration [7-9]. The infiltration is commonly used method in which a porous-sintered tungsten skeleton is filled with melted copper. However, in this technique, the pores, copper pools and also the agglomeration of tungsten are easily formed [8]. These defects lead to the degradation of the W-Cu composite's properties. Liquid phase sintering (LPS) is the next popular method to produce W-Cu composites. This technique consists of three steps; mixing W and Cu powders by mechanical milling, compressing the mixture powders and follows by sintering at the temperature higher than melting point of Cu [1, 2]. But, liquid phase sintering may result in the coarse grain growth of W during sintering and it is difficult to obtain the full density of the specimens because of the poor solubility and wettability between W and Cu.
Conclusion
In this work, W-50Cu composites have been produced by powder route using spark plasma sintering technique. The effect of the sintering temperature and heating rate on the structure and mechanical properties of the sintered has been investigated. The conclusions are as following:
The increase of sintering temperature led to the higher density, larger W particles and resulted in the better strain at break of sintered samples. The Vickers hardness has been improved with the rising temperature from 900 to 950 oC, but further increase of sintering temperature caused the reduction of Vickers hardness.
On the contrary, the faster heating rate led to the reduction of density and smaller average W particle size. In addition, the higher heating rate also led to more residual pores in the W-50Cu structure and therefore, lowers the strain at break of sintered sample. The Vickers hardness shows an increase with heating rate. This could be due to the smaller average particle size of W particles in Cu matrix.