Powder Metallurgy Sintering TZM Alloy Carbide Forming Characteristics
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- Category: Molybdenum knowledge
- Published on 10 December 2015
- Written by yiping
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Comparing the sintering TZM alloy and smelting TZM alloy’s micro-structure found sintering TZM alloy has following characteristics are as below:
1. Powder metallurgy sintering TZM alloy’s sintering temperature is far lower than smelting temperature which is a kind of microscopic diffusion and uneven sintering body.
2. During solid state sintering the main diffusion are slow, especially when Zr atom’s diameter is bigger than Mo. Even alloy sintered at about 1940℃there are still some simple substance doesn’t diffuse into substrate.
3. The TiC which produced by powder metallurgy sintering TZM alloy is mainly in grain boundary and it is in situ reaction.
According to the mixed powder characteristic of powder metallurgy, the reaction during sintering should priority react at phase interface of particle aggregation. With densifying of sintering and element’s solid solution diffusion, there will happen carbide reaction formation in grain boundary, subboundary or between aggregation particle where alloy element are easy diffusion. Final, at the high temperature, Ti and Zr become solute and enter into molybdenum substrate and during cooling process will react with precipitation C atom to form intracrystalline carbide.
The solubility of C atom at 2200℃ eutectic temperature in molybdenum is 0.12%~0.14%( mass fraction). At 1500℃ the solubility of it is 0.005%~0.010% and at the room temperature is zero. So during cooling process of powder metallurgy TZM alloy there still has small amount of TiC. Because the solubility of C atom reduce and it will react with Ti atom which is in the grain
internal. If there doesn’t have Ti atom then C will react with Mo to form Mo2C. The diameter of Zr is 1.15times than Mo’s so diffusion is more difficult. According to the characteristic of micro-structure, some Zr will exist in simple substance and other Zr at the high temperature will from solid solution with Mo and during cooling process will separate out Laves phase Mo2Zr. And at the edge the C atom will react with Zr to form ZrC by in situ reaction and grain inner is hard to form ZrC.
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