The aim of the present study was to characterize the repair weld of serviced (aged) solid-solution Ni-Cr-Fe-Mo alloy: Hastelloy X. The repair welding of a gas turbine part was carried out using Gas Tungsten Arc Welding (GTAW), the same process as for new parts. Light microscopy, scanning electron microscopy, transmission electron microscopy, microhardness measurements were the techniques used to determine the post repair condition of the alloy. Compared to the solution state, an increased amount of M 6 C carbide was detected, but M 23 C 6 carbides, sigma and mu phases were not. The aged condition corresponds to higher hardness, but without brittle regions that could initiate cracking.

Eight investment castings of Inconel 713C superalloy were fabricated, varying in the melt-pouring temperature, from 1400 to 1520°C, and CoAl 2 O 4 inoculant content, 0 or 5 wt.%, in the primary coat. Their influence on grain size on tensile and creep properties was investigated. The best combination of yield stress (815 MPa) and elongation (A 4 = 7.65%) at ambient temperature was obtained in surface-modified castings poured from 1520°C. The longest time to rupture was for the unmodified castings (76.8 h) poured from 1520°C, while for the modified variant, the time to rupture was lower around, 7.4 h, which was still a satisfactory value. During tensile testing, microcracks were formed in large eutectic c¢, carbides and borides, due to the accumulation of stress at interfaces with the matrix. During creep, N-type rafting of c¢ precipitates and phase transformation MC + c fi c¢ + M 23 C 6 took place.

The aim of this study is to investigate influence of selected parameters of gas tungsten arc welding on microstructure of MAR-M247 nickel based superalloy originating from turbine vane. MAR-M247 is a precipitation-strengthened superalloy which is widely used in aerospace engines. The main strengthening phase in this material is ordered L1 2 intermetallic γ' phase Ni 3 (Al, Ti). The surface of alloy was modified by electric arc in order to present microstructural changes in weld and heat affected zone. Investigation of the heat affected zone revealed that constitutional liquation of γ' particles and primary carbides is responsible for the formation of a liquid grain boundary layer which finally contributed to cracking. Scanning electron microscopy indicated high susceptibility to cracking of MAR-M247 alloy which is connected with high content of γ'-formers aluminum and titanium.

The effect of cobalt aluminate inoculant addition and melt-pouring temperature on the structure and mechanical properties of Ni-based superalloy was studied. The first major move to control the quality of investment cast blades and vanes was the control of grain size. Cobalt aluminate (CoAl 2 O 4 ) is the most frequently utilized inoculant in the lost-wax casting process of Ni-based superalloys. The inoculant in the prime coat of moulds and pouring temperature play a significant role in grain size control. The finest surface grains were obtained when the internal surface of shell mould was coated with cobalt aluminate and subsequently pouring was at 1480°C. The influence of selected casting parameters and inoculant addition on mechanical properties was investigated on the basis of tensile, creep and hardness testing. The effect of grain refinement on mechanical properties were consistent with established theories. Tests conducted at ambient temperature indicated a beneficial effect of grain refinement both on tensile strength and hardness. In contrast at elevated temperature during creep, the reverse trend was observed.