| With the rapid development of science and technology,modern industry and some high-end applications have become more and more urgent for new materials with high temperature resistance,oxidation resistance and corrosion resistance.Iridium(Ir)is a platinum group element with a melting point of up to 24470C.It has excellent corrosion resistance and high temperature thermal stability.Rhodium(Rh)is also a platinum group element with melting point 1963 ? and it is next to Ir and Os in the platinum group elements.The lattice constants of both are close and solid solution can be formed in the whole composition range.Adding rhodium to iridium can greatly improve the high temperature oxidation resistance of iridium,so Ir-Rh alloy is an ideal material for the use in ultra-high temperature condition.HIP is a new powder metallurgy technology developed in recent decades with some unique advantages that the other processing methods do not have.The parts treated by HIP have uniform microstructure and good mechanical properties widely used in special fields such as aeronautics and astronautics.In this paper,the effect of Rh content on the mechanical properties of Ir-Rh alloy was studied by using the first principles method based on density functional theory.We also have studied the behavior of Ir-Rh alloys with different Rh compositions under high temperature oxidation conditions.The alloy composition was screened according to the experimental results.The theoretical calculation results show that the strength and hardness of Ir-Rh alloy increase rapidly with the increase of Rh content.After reaching the maximum at Ir-10 Rh,the Rh drops rapidly to Ir-40,then slowly rises and then decreases slowly.The addition of Rh can lead to embrittlement of Ir-Rh alloy,and its brittleness increases first and then decreases with the increase of Rh content,and reaches the maximum at Ir-50 Rh.The high temperature oxidation resistance of Ir-Rh alloys increases with the Rh content because the Rh element can reduce alloy oxide volatility thus forming a layer of oxide film on the alloy surface to protect the internal metal.Considering the results of theoretical calculations and oxidation experiments,we chose Ir-20Rh as the alloy component of the process route.In order to find the best mixing powder and degassing process,the influence of mixing time,small ball and degassing temperature on the properties of metal powder was studied by designing different mixing technology and degassing process.The process of Ir-Rh alloy is CIP-Sinter-HIP.The density and micro structure of iridium rhodium alloy obtained by hot isostatic pressing at different temperatures and pressures were also analyzed and characterized.In the experiment of mixing iridium and rhodium alloy,it is found that the time required for the mixture to achieve uniform with the ball is shorter than that without.The oxygen content of the mixed powder obtained by the two processes is fairly constant.The nitrogen content of the metal powder obtained by mixing with the ball is slightly higher than that without mixing with the ball,but it can be reduced to below 0.001%after the degassing process.So the mixing process chooses to mix with the ball.After two hours of gas removal at 1200 'C,the temperature is increased t0 1800? to sinter.With the increase of temperature and pressure of hot isostatic pressing,the density of alloy will increase.But by the coating material limit,even with the highest temperature(1300?)and the maximum pressure of hot isostatic pressing(140MPa)two hours,the density increased to 95.7%.So we will repressing it at higher temperatures that it can increase to the theoretical value. |
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