Microstructure and Plastic Deformation of the As-Welded Invar Fusion Zones
- PDF / 3,129,595 Bytes
- 8 Pages / 593.972 x 792 pts Page_size
- 0 Downloads / 177 Views
ODUCTION
THE Invar effect has existed since the discovery of Fe65Ni35 Invar by Guillaume in 1897.[1] Traditionally, it has been used primarily in precision-measuring devices.[2] Recently, Invar has been used for cryogenic liquid-transfer systems and aircraft tooling.[3] Potential application of Invar includes its use as an additive in dissimilar welds.[4] However, Invar is prone to cracking or micro-cracking if it is not protected properly[5] or after it is deformed.[6] Therefore, it is significant to further understand the microstructure, crystal structure, and plastic deformation mechanism for Fe-Ni Invar. The eutectic microstructure is thought to result from a decrease in sulfur concentration and the locking of intergranular slip.[7] Hsu et al.[8] suggested that a lowering of the martensitic transformation temperature resulted from the pinning of clustered vacancies to partial dislocation. Hongoh et al.[9] investigated the effects of alloyed elements on microstructures and ductility dip cracking
D.J. YAO and D.R. ZHOU are with the College of Materials Engineering, Shanghai University of Engineering Science, Shanghai, 201620, China. P.Q. XU is with the College of Materials Engineering, Shanghai University of Engineering Science, Shanghai, 201620, China, and also with the Shanghai Key Laboratory of Materials Laser Processing and, Modification, Shanghai Jiao Tong University, Shanghai, 200240, China. Contact e-mail: [email protected] F.G. LU is with the Shanghai Key Laboratory of Materials Laser Processing and, Modification, Shanghai Jiao Tong University, Shanghai, 200240, China. Manuscript submitted August 17, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
susceptibility in multi-pass weld metals of Invar. The microstructure changed from a cellular structure with straight grain boundaries to a cellular dendritic structure with saw-teeth grain boundaries. The eutectic microstructure in the weld metal is thought to result from a decrease in sulfur concentration in the grain boundary and the locking of intergranular slip by the anchoring effect of the cellular dendritic structure. Similarly, friction stir-welded Invar has a homogeneous coarse austenite microstructure in the stir zone.[10] The microstructure changes from room temperature to 1100 K (827 C) in the as-milled Invar alloys were investigated, and phase transformation in heating–cooling processes was characterized.[11] The results showed that the initial as-milled Invar exhibited a majority phase with fcc crystal structure and a minority phase with body-centered cubic (bcc) crystal structure. Heating above 850 K (577 C), structural phase transformation of the bcc phase into fcc was observed. However, no transformations occurred during further heating or cooling down. Another face-centered tetragonal (FCT) martensite was also observed in Invar alloys.[12] Schramm et al.[13] investigated the stacking fault energies of the fcc Fe-40 wt pct Ni Invar to pure Ni. The low nickel alloys exhibited anomalous reductions in the lattice parameter after cold work, which was
Data Loading...
