Rare Earth Doped TZM Alloy

Introduction

TZM alloy is the most widely used molybdenum alloy, which has many excellent properties, often used to make high-temperature structural parts used in different fields. With the industrial development, it has a further request on TZM alloy properties. Doped a small amount of rare earth elements in TZM alloy can reduce grain size, plastic-brittle transition temperature, improving the recrystallization temperature, high temperature strength, ductility and high temperature creep resistance. Doped with a small amount of rare earth elements can not only improve the performance of the alloy, but also to expand its application range. Common rare earth doped elements are La and Re. Doping with La and Re oxides, produced by the powder metallurgy method, obtain La2O3-TZM alloy and Re-TZM alloy.

Property Analysis

La2O3-TZM alloy mechanical properties: The tensile strength of La2O3-TZM alloy improved 119MPa than undoped TZM alloy, and yield strength improved 49MPa, elongation rate increased by 4.3%. This is mainly because dispersed La2O3 has strong dispersion strengthening effect, and La2o3 will effect dislocation as well, so La2O3-TZM alloy has higher strength. In addition, the second phase particles is smaller than TZM alloy’s, more evenly distributed, so the plastic deformation resistance, high yield strength is large. Overall, it has good mechanical properties than TZM alloy.
La2O3 TZM alloy fracture morphology: fracture morphology of TZM alloy is brittle intergranular fracture, and La2O3-TZM alloy is mixed dimples-quasi-cleavage fracture. Dispersed La2O3 particles uniformly distributed in the grain boundary and crystal interior, causing interfacial surface area increases. Oxygen, carbon, nitrogen and other impurities will preferentially gather at grain boundaries and La2O3 particle surface, which will greatly reduce the impurity concentration and enhance the grain boundary bonding strength, to improve the toughness of TZM alloy.
TZM-Re alloy performance analysis: Re element plays a powerful "rhenium" effect in TZM alloy. Doped with Re can not only improve the high temperature properties of the alloy, but also can improve the properties of the alloy at room temperature. With Re doped amount increase, TZM alloy’s bending strength has not significantly improved. Mainly because the alloy material is not completely occur plastic deformation before fracture. In general, the strength of Re-TZM alloy is slightly lower, but TZM-Re alloy exhibits a certain degree of toughness at room temperature.