Effect of Cobalt on Microstructure and Mechanical Properties of Invar Alloy
Due to low coefficient of thermal expansion (CTE), Invar alloy is widely used in Liquefied Natural Gas (LNG) carrier, long distance transmission lines and so on. However, the coarse grain and low hardness restrict the further application. In the present study the samples were prepared by vacuum arc furnace. The effect of cobalt on microstructure and mechanical properties were explored. The results showed that the microstructure without cobalt was mainly composed of coarse columnar crystals with heterogeneous dimension distribution, and average grain area was 289 μm × 189 μm. For the sample with 0.2 wt% cobalt the microstructure was more uniform and the average grain area was 260 μm × 166 μm. In addition, lots of cellular substructure formed in the columnar dendrite with different shapes dislocation etch pits. The CTE decreased with the addition of cobalt, especially when the content of cobalt was 0.2 wt%. Compare to the sample without cobalt the microhardness with cobalt addition of 0.2 and 4 wt% are 193 and 170 HV, increased by 25 and 10% respectively. It can be concluded that the microstructure and mechanical properties can be changed by controlling the content of cobalt under the condition of rapidly cooling condition.
KeywordsInvar alloy Vacuum arc melting Crystalline organization Grain area Hardness
The present authors are thankful for the financial support provided by National Natural Science Foundation of China (No 51304059).
C. X. Chen: designing the experiment approach and executing part of the experiment processing; B. J. Ma: executing most part of the experiment processing; S. N. Miao: for mechanical property test; B. X. Liu: for theoretical analysis.
Conflicts of Interest
The authors declare no conflict of interest.
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