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The microstructure and mechanical properties of a 90W–7Ni–3Fe heavy alloy manufactured using laser melting deposition (LMD) have been investigated with a goal of understanding the LMD process and the relevant strengthening mechanisms. A reference sample prepared using liquid phase sintering (LPS) with similar composition has been used for comparison to isolate effects of the processing rate. The results show that the nearly fully-dense LMD sample consists of two periodically alternating sublayers containing different volume fractions of W particles. Compared to the reference LPS sample, the LMD sample has a higher W content in the binder matrix, a more refined microstructure, a higher dislocation density and a lower contiguity between W particles. Furthermore, the LMD sample has a yield strength of 822 ± 30 MPa, which is about 200 MPa higher than that of the reference LPS sample. This strength difference is quantitatively analyzed based on the microstructural observations. It is shown that the increased fraction of W-matrix interfaces, a higher interface bonding strength and more pronounced constraint effects, resulting from the higher processing temperature and fast cooling of LMD, provide extra strengthening. The present study provides an important basis for optimizing the LMD process for manufacture of high W content tungsten heavy alloys with improved mechanical properties.

The selective grinding of bauxite was investigated experimentally in ball and vibration mills, using a low-grade ore with aluminium to silicon ratio (A:S) of 4.4. Grinding efficiency, particle size distributions of ground products and distribution of alumina and silica were studied under various grinding conditions and optimal values for the parameters determined. The findings are discussed in terms of the mechanisms both of mineral liberation of diaspore from silicate minerals and of size reduction, as well as the influence of the operating parameters: grinding fineness, grinding pulp concentration, and ratio of grinding media to charge. For the ball mill and vibration mill respectively, the weight ratios of ground product with A:S greater than 7.5 are 27% and 25% and the recoveries of Al2O3 are 30% and 27%., The selective grinding of bauxite was investigated experimentally in ball and vibration mills, using a low-grade ore with aluminium to silicon ratio (A:S) of 4.4. Grinding efficiency, particle size distributions of ground products and distribution of alumina and silica were studied under various grinding conditions and optimal values for the parameters determined. The findings are discussed in terms of the mechanisms both of mineral liberation of diaspore from silicate minerals and of size reduction, as well as the influence of the operating parameters: grinding fineness, grinding pulp concentration, and ratio of grinding media to charge. For the ball mill and vibration mill respectively, the weight ratios of ground product with A:S greater than 7.5 are 27% and 25% and the recoveries of Al2O3 are 30% and 27%.