Effect of processing parameters on the microstructure and mechanical properties of wide-gap braze repairs on nickel-superalloy René 108

Abstract

Gas turbine components experience large temperature gradients due to thermal cycling that often result in cracking. When brazing wide gaps greater than 500 μm in width, capillary action is inadequate to fill the joint and activated diffusion healing (ADH) is applied for repairs. ADH utilizes a mixture of a low melting temperature filler metal and an additive powder with a composition similar to that of the base metal. This research studies the effect of processing parameters on the microstructure and mechanical properties of repaired joints on DS Rene 108 superalloy. AWS BNi-2 and BNi-5 grade filler metals were mixed with MAR-M 247 alloy powder at weight percent ratios of 40:60, 50:50, and 60:40. For BNi-2 containing brazes, the mechanical properties improved with increasing additive powder. In contrast, the BNi-5 containing brazes showed an opposite trend. Brazing temperatures were held at 1200°C and 1232°C. The mechanical properties for both braze alloys improved at the higher brazing temperature. Diffusion hold temperatures were held at 1100°C and 1121°C for 2 h and 4 h. For the BNi-2 alloys, the higher temperature and longer brazing time improved mechanical properties. For the BNi-5 alloys, the lower brazing temperature and shorter brazing time improved mechanical properties.