Effect Of Mo, Mn On Structure And Properties Of Tungsten Products

As one of the most important strategic resource around the world, tungsten (W)has been widely used in aerospace, electronics, metallurgy and other fields for thenatures of high melting point, high hardness and low vapor pressure. Therefore, it hasimportant theoretical and practical significance to do the research on effect ofimpurities on the structure and properties of tungsten products, especially upon theefficient use of our tungsten resources and the preparation of high performancetungsten products.The effect of Mo, Mn (which have the solid solubility in the W) on tungstenproducts’ structure and properties was studied in this paper, detailly from the effectson the calcination of ammonium paratungstate (APT), the reduction of tungstenoxide(WO3), the carbonization of tungsten (W) and the Sintering of tungsten carbides(WC+Co) with different percentage of Mo, Mn. The evolution and distribution of Mo,Mn during the preparation of tungsten products were investigated. The structure andproperties of tungsten products with the variation of impurity elements weresummarized. The last but not the least, the mechanisms of Mo, Mn in the preparationof tungsten products were revealed.The growth models of W and WC were reasearched using the thermodynamiccalculation and simulation. The influence mechanism of Mo, Mn on W and WC graingrowth were presented, which explained the experimental phenomena very well, andthe research presented important references for practical industrial production. Thebelow results were obtained from this paper:1. The commercially APT with different content of (NH4)6Mo7O24(AHM) wasprepared in the liquid-solid doping method. Mo experienced the evolution ofMoO3—(Mo, W)—(Mo, W)C during the calcination of APT, the reduction of WO3and the carbonization of W. During the hydrogen reduction of WO3, the grainangularity was inactivated with the addition of Mo, and the morphology was changedfrom polyhedron to spherized compared with that of undoped W particles.With theincrease of Mo, the size of W particles was remarkably decreased, and the average size of10000ppm Mo-doped W particles was0.30μm compared that of undoped Wparticles. The morphology won’t change too much During the carbonization of W.Meanwhile, the size of Mo-doped WC particles was slightly decreased. The averagesize of undoped WC particles was0.57μm, the WC particles doped with10000ppmMo while the average size was0.38μm. The mechanisms of Mo on refinementof W and WC particles were pointed out: Mo which evenly distributed solubilized inW and WC, resulted in deformation of crystal lattice, and the formation anddevelopment of particle surface steps were prevented, Mo played a role in refining Wand WC particles. In addition, the distribution of Mo was always in the small WCparticles. The density and hardness of Mo-doped YG6alloy was decreased slightly.3. The commercially APT with different content of MnCl2was prepared by theliquid-solid doping method. Mo experienced the evolution ofMn2+WO4—Mn2+WO4—(Mn, W)C and Mn5C2during the calcination of APT, thereduction of WO3and the carbonization of W. During the hydrogen reduction ofWO3, the grain angularity was inactivated with the addition of Mn. With the increaseof Mn, the average size of undoped W particles was1.14μm, the W particles dopedwith10000ppm Mn while the average size was0.41μm; Mn which distributed inand out of W influenced the formation and growth of crystal nucleus, refined Wparticles. During the carbonization of W, the size of WC particles was slightlydecreased with the addition of Mn. The average size of undoped WC particles was0.57μm, the WC particles doped with10000ppm Mn while the average size was0.35μm; the growth of WC was influenced with Mn5C2and Mn which solubilized inWC. In addition, the distribution of Mn was always in the small WC particles and Co.The density and hardness of Mn-doped YG6alloy was decreased slightly.