| This paper includes two parts, Study on Preparation and Micro structure Property of Precipitation Strengthening Cu Alloy. Boron and tungsten to replace the expensive Nb elements, and were added to Fe-Cr-C hardfacing alloy and its effect on the microstructure and microhardness of the alloy was studied. The main research contents are as follows:1. The influence of cold-worked and aging processes on the microstructures, mechanical properties and conductivity of Cu-Cr-Y alloy has been investigated. Cu-Cr-Y alloy has an excellent combination of microhardness and conductivity after cold working70%and aging at480℃for24min. The microhardness and conductivity is about143HV and84%IACS, respectively. There were two particles in the Cu-Cr-Y alloy:the coarser particles exist in the Cu-Cr-Y alloy before aged, the fine and dispersed distributed Cr precipitate, which form due to decomposition of the supersaturated solid solution during aging, is responsible for the peak maximum microhardness as it is predominantly present in the peak aged hardening condition.2. Two kind processing crafts to the casting Cu-0.8Cr-0.05Y alloys:casting+cold working+aging, and casting+solution treated+cold working+aging. The alloy after treated by casting+cold working+aging has more excellent properties because the second phase precipitates from the alloy and grows up before recrystallization during aging. The hardness and conductivity of the alloy are up to150HV and90%IACS respectively by cold working90%and aging at480℃for30min.3. The Cu-0.8Cr-0.05Y alloys containing different contents of Zr additions were treated with cold working and aging. Zr addition could obviously improve microstructures, refine grain boundary, decrease the eutectic of Cu-Cr alloy, increase the hardness and thermal stability. The addition of Zr was found to refine Cr particles and made Cr particles growing more slowly during aging, thus the strength of the alloys were improved. The hardness and electrical conductivity of the alloy cotaining 0.2%Zr addition are198HV and81%IACS respectively by cold worked90%aged at480℃for60min, has good combination of hardness and electrical conductivity.4. As-cast Microstructure of Cu-1.0Cr-0.3Zr-0.05Y Alloy was studied. The results show that as-cast microstructure of Cu-1.0Cr-0.3Zr-0.05Y alloy were dendritics; there are Cu matrix and primary of Cr inside the crystal. Rare earth Y distributed in grain boundaries and exists in form of Y2O3、Cu5Y. The existence of Y2O3can purify copper matrix. In the grain boundary there are Cu2O、Y2O3、Cu5Y、 Cu5Zr phase and complex eutectic structure. Comparison of Cu-1.0Cr-0.05Y and Cu-1.0Cr-0.3Zr-0.05Y alloy in different heat treatment of aging characteristics. Solution treatment could increase the effect of the aging treatment and result in decrease in the hardening of the alloys. The addition of Zr was fourd to refine the Cr particles and grow more slowly the Cr particles during the aging.5. Based on the above findings, choose good comprehensive performance and oxidation behaviour of Cu alloys with high performance were studied. Add a Zr element, aging precipitation dispersed Cr, Zr the second phase, is conducive to the formation of homogeneous Cr2O3film at400℃; The alloy with Zr antioxidant is not evident at550℃.The reason may be due to the oxidation temperature is higher than the aging temperature, small Cr, Zr particles further aggregation and growth during the aging of550℃, so as to form a continuous selective Cr2O3oxidation ability is relatively poor, reducing alloy oxidation resistance. The effects of grain refinement on oxidation resistance of the alloy. With low content of Cr, Zr is not easy to form a protective film at grain boundary; and at550℃the recrystallized grain refinement will speed up effect on oxidation of copper is550℃. Recrystallization grain growth, the grain boundary diffusion ratio decreases.In addition, this paper also conducts the following research work:The Nb was substituted in the A2#specimen for expensive. To prepare composite addition of W, B hardfacing flux cored wire, and its microstructure and properties were analyzed.1. The first comparison of two commercially available for wear resistant hardfacing flux-cored wire structure and properties, including Nb A2#sample performance better master, based on the following factors:the first NbC hardness higher than the M7C3microhardness reaches as high as44%, distribution around the M7C3or embedded therein, the wear-resisting framework supporting role; the second carbon content and niobium instead of a portion of the chromium content increases, alloy composition deviation of eutectic line farther, in the eutectic reaction process, primary phase ratio is more, eutectic structure in solidification structure proportion of corresponding reduced, thus increasing the primary carbide eutectic structure corresponding to the less, the hardness increase is one of the important reasons. In addition Nb on eutectic carbide and matrix of thinning effect on performance improvement of a certain contribution.2. With the addition of W, B, the microstructure of hardfacing alloy was increased the M7C3type primary carbide. Because W, B can form carbides, and can be dissolved in solid solution, except can increase tungsten carbide, boron carbide reinforcing phase reinforced matrix hardness number, also because the two element can be solid solubility in austenite, to increase the stability of austenite, resulting in the cooling process of the sample matrix martensite amount increases, the corresponding matrix hardness elevated.Including W, B B1#specimen overlay surface hardness up to60.8HRC, and A2#Nb containing considerable.W, B due to replace the expensive metal Nb can greatly reduce the production cost, and the performance is not reduced. |
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