Effects Of La₂O₃/ZrC Ceramic Composites On The Mechanical Properties And Microstructure Of Tungsten Alloy

Carbide enhanced tungsten alloys and ODS tungsten alloys which naintain good mechanical properties and creep resistance at elevated emperature have become the most promising high-temperature materials. However, the strengthening effects of single phase has its limitations. Moreover, two-phase or multiphase collaborative strengthening can display each phase’s advantages.First of all, by compounding La2O3/ZrC ceramic composites to strengthen tungsten, oxides/carbide collaborative strengthening elevated tungsten alloy can be prepared in this paper. La2O3coated ZrC composite was prepared by means of heterogeneous precipitation method. Factors affecting the preparation procedure and phase transformation was analyzed to obtain the optimal process. And morphology, structure, particle size and encapsulation efficiency of the coated composites were characterized to figure out what the mechanism of the heterogeneous precipitation coating process could be.On that basis, adding the coated composite reinforcement into tungsten matrix in propertion, so as to sinter collaborative strengthened tungsten alloy. Tensile strength of the alloy at room temperature was tested. And alloys’microstructure and mechanical properties of different second-phase addition were observed and studied. Finally, how the changes of sintering behavior, density and linear shrinkage of the alloys influence on the relative content of coating phase composition are analyzed and discussed. The results showed that:(1) The optimal preparation process of core-shell La2O3/ZrC nanocomposite powder by using heterogeneous precipitation method is: for the final reaction solution system pH=10, volume percentage of dispersion media PEG400being added into solution system was0.8%and coated powder precursor was calcined at750℃for2h. The coated powder particles reflected the characteristics of core-shell structure apparently, and the surface of particles represented chemical property of La2O3. And the formation mechanics of coated composites experienced out of phase nucleating and homogeneous growing. (2) Coating treatment and content of the secend-phase shows a greater impact on the mechanical properties of W-ZrC/La2O3alloy. Tensile strength of W-2ZrC/3La2O3alloy was450Mpa, which has nearly50percent increase in strength than un-coated W-2ZrC-3La2O3alloy, sintered at1950℃for2h. Comparing to W-6ZrC alloy, W-6ZrC/xLa2O3alloys’strength improved up to about370Mpa, which increased by31%and32%respectively, with the addtion of0.5%and3.0wt%La2O3.(3) The way of compound adding can improve the uniform distribution of ZrC/La2O3in alloys, form second phase particles in the sintering process which would obstruct the effects of migration, detail the grain, and make alloy strength increased. Composite phase particle distribution in grain boundaries, and the EDS analysis results showed that composite phase constitutes W, Zr, La, C and O elements.