Ignition-proof mechanism of magnesium alloy added with rare earth La from first-principle study

The surface segregation of La and its effect on the oxygen adsorption on a Mg(0001)surface for a coverageΘ=0.25 monolayer were performed by using first-principles calculations.The calculated results showed that La atoms preferred occupying surface sites to the bulk sites,which suggested the La surface segregation.When oxygen atoms adsorbed on a pure or La alloyed Mg(0001)surface,certain amount of heat would release,and La alloying made the heat released less,which might increase the ignition point of Mg alloy.Both Mg and La had strong atomic affinity with oxygen,so the oxidation film of Mg-La alloys consisted of MgO,La2O3.The denser La2O3 turned oxide film into fine and close structure,and prevented oxygen from passing through the oxidation film.The La-O covalent bonding could explain why La2O3 was compact,and resulted in good ignition-proof of Mg-La alloys.     

晶粒尺寸对316L不锈钢在模拟人体体液环境中腐蚀行为的影响

为提高医用金属材料的耐腐蚀性能,以一种商用316L不锈钢为研究对象,采用冷轧及退火工艺制备了平均晶粒尺寸为198 nm的超细晶(UFG)、776 nm的亚微米晶(SMG)和1.18μm的细晶(FG)试样,通过电化学实验测定了不同平均晶粒尺寸试样在模拟人体体液中的动电位极化曲线和电化学阻抗谱。结果表明：腐蚀电位和击穿电位随着平均晶粒尺寸的减小而增大,UFG试样具有较高的腐蚀电位(-0.38 V_SCE)和击穿电位(-0.03 V_SCE);电容半径随晶粒尺寸的减小而增大,晶粒细化后,316L不锈钢在模拟人体体液环境中的耐腐蚀性能得到提高。其中,退火温度750℃条件下保温5 min制备的平均晶粒尺寸为198 nm的超细晶316L不锈钢在模拟人体体液环境中具有最佳的耐腐蚀性能。