Superalloy Joints Research Articles

Microstructure and mechanical properties of partial transient liquid phase bonded Si3N4–DZ483 superalloy joints

Partial transient liquid phase bonding (PTLPB) was applied to silicon nitride/nickel-based superalloy (DZ483) joints using Ti/Cu/Ni interlayers. Microstructure examination and mechanical properties evaluation of the joints show that bonding of Si3N4 to superalloy was successful. A uniform compact reaction layer about 2.7μm thickness was found at the Si3N4/Ti interface, which was formed by the reaction between Ti and Si3N4 substrate. With joining temperature rising, the flexural strength of the joining samples increased initially and then decreased. When the joining temperature was 1323K, the flexural strength of the joints reached to 170MPa. The fracture behavior of the joints was also discussed, with the ceramic reaction layer being the region where all failures occurred.

Stress analysis and fatigue life estimation for four types of super-alloy-welded joints

By means of the finite element analysis software ANSYS, the stress concentration coefficient of four kinds of super-alloy welded joints, namely, normal butt welding, dislocation butt welding, non-isopachous butt welding and new material butt welding, were calculated. With the method of group comparison, the relationship between these calculated results and real fatigue life was analysed. It is estimated that the fatigue life of the non-isopachous butt-welded joint had an increase of 1.22?2.09 times that of normal butt-welded joint at the stress load of 520 MPa, and that of the normal butt-welded joint of a new material, GH4033, increased 2.16?3.54 times at the same stress level. The SEM fracture analysis revealed that slag, micro-cracks on the surface of weld seams or at the weld toes, and the brittle secondary particles were the dominant factors in cutting down fatigue life.

酸化物分散強化型耐熱超合金のパルス通電焼結接合継手の機械的特性

In order to evaluate the mechanical properties of ODS superalloy joints bonded by pulsed electric-current sintering (PECS) technique, the tensile test at elevated temperature and creep rupture test were conducted for MA956 (Fe-based ODS alloy) and MA754 (Ni-based ODS alloy) joints. The ODS superalloys were bonded at 1323-1373 K for 0.9-64.8 ks in vacuum. The tensile properties at elevated temperature of completely densificated joints were almost comparable to those of base metal. However, the creep rupture lives of joints could be improved by the further holding at bonding temperature after the fully densification. The creep rupture lives of joint bonded for 64.8 ks reached about 70% of longitudinal directional life of base metal. TEM observations revealed that Cr2O3 inclusions existed on the prior particle boundary (PPB), and percentages of Cr2O3 inclusions on PPB were decreased with increasing the bonding time. The strengthen particles of oxide(Y2O3) were uniformly dispersed in the whole area of bonded interlayer without coagulating and coarsening. These results suggested that the improvement in creep rupture strength with bonding time was mainly attributed to the amelioration of the bonding strength of PPB.

High Temperature Low-Cycle Fatigue of Friction Welded Joints-Type 304-304 Stainless Steel and Alloy 718-718 Nickel Base Superalloy

This paper assesses the high-temperature low-cycle fatigue of the Type 304 stainless steel and Alloy 718 superalloy friction-welded joints. Strain controlled low-cycle fatigue tests for 304-304 and 718-718 friction-welded specimens were carried out at 923K in air to obtain the fatigue strength of the joints. These materials were selected as the cyclic hardening and softening materials, respectively. The 304-304 welded specimens showed inferior fatigue strength in comparison with the base metal while the 718-718 specimens exhibited fatigue strength equivalent to that of the base metal. The difference in the fatigue strength between the two materials is discussed from the viewpoint of the cyclic deformation behavior and strain reduction at weld interface.