Hot cracking in cast alloy 718

Abstract

Hot cracking susceptibility of the Fe-Ni-based precipitation hardening cast superalloy Alloy 718 was studied by Varestraint weldability testing. The effect of two hot isostatic pressing (HIP) treatments commonly employed in the aerospace industry was investigated in reference to the as cast condition. It was found that the heat affected zone (HAZ) liquation cracking susceptibility increased for samples with pre-weld HIP treatments. The as cast condition disclosed the best response for liquation cracking followed by HIP-1120 (1120°C/4h (HIP) + 1050°C/1h and furnace cooling to 650°C/1h in vacuum + 950°C/1h) and HIP-1190 (1190°C/4h (HIP) + 870°C/10h and furnace cooling to 650°C/1h in vacuum + 950°C/1h). The amount of the secondary precipitates and base metal grain size was found to be important parameters influencing the cracking susceptibility. Regarding solidification cracking susceptibility, the three conditions appear to behave similarly.

Heat-Affected-Zone Liquation Cracking in Welded Cast Haynes® 282®

“…The results from HAZ crack measurements are plotted in Figure 7. Despite the large scatter, which is typical in testing of cast materials, as reported in previous studies [11,12], it can be seen that cracking-behavior results are similar for the preweld heat treatments at 1120 • C and 1160 • C, which exhibited the least amount of cracking, whereas the 1190 • C heat-treatment condition exhibited the highest amount of cracking. Base-metal hardness did not experience significant change after heat treatment, with hardness level in the range of 215-230 HV in the heat-treated conditions, and about 245 HV in the as-cast condition (Figure 4).…”

“…aforementioned preweld heat treatment temperatures were investigated for the cast Alloy 718 [12] and ATI ® 718Plus TM [13]. Even though Haynes ® 282 ® is devoid of detrimental Laves phases, a common heat treatment for the three superalloys that minimizes cracking is interesting from an industrial perspective.…”

“…Grain-boundary segregation was examined by a CAMECA NanoSIMS 50L secondary ion mass spectrometer (CAMECA, Gennevilliers, France) using a primary beam of Cs + . Mass-resolved images were obtained for 11 B − , 12…”

“…Generally, for Fe-Ni and Ni-based superalloys, preweld temperatures are decided so that incipient melting of the low-melting Gamma-Laves eutectic is avoided, which occurs in the range of 1150-1160 • C. This is generally carried out by two different hot isostatic pressing (HIP) approaches, commonly employed in the aerospace industry, at 1120 • C and 1190 • C [9][10][11], respectively, below and above the melting of the Laves eutectic. The aforementioned preweld heat treatment temperatures were investigated for the cast Alloy 718 [12] and ATI ® 718Plus TM [13]. Even though Haynes ® 282 ® is devoid of detrimental Laves phases, a common heat treatment for the three superalloys that minimizes cracking is interesting from an industrial perspective.…”

Influence of Heat Treatments on Heat Affected Zone Cracking of Gas Tungsten Arc Welded Additive Manufactured Alloy 718

“…The wrought Alloy 718 had an average grain size of around 25 µm. Grain size of the cast material is not clearly shown in Figure 14c, but another study [16] regarding hot cracking in cast Alloy 718, showed that the average grain size of as cast base metal was around 1700 µm. Thus, it could be expected that SLM-manufactured material in the as-built condition and wrought material would have similar cracking sensitivity, while as cast material would be much worse.…”