Precipitation of an intermetallic phase with Pt2Mo-type structure in alloy 625

Abstract

The microstructure of Alloy 625, which has undergone prolonged (ϳ 70,000 hours) service at temperatures close to but less than 600 ЊC, has been characterized by transmission electron microscopy. The precipitation of an intermetallic phase Ni 2 (Cr, Mo) with Pt 2 Mo-type structure has been observed in addition to that of the ␥" phase. Six variants of Ni 2 (Cr, Mo) precipitates have been found to occur in the austenite grains. These particles exhibit a snowflake-like morphology and are uniformly distributed in the matrix. They have been found to dissolve when the alloy is subjected to short heat treatments at 700 ЊC. The occurrence of the Ni 2 (Cr, Mo) phase has been discussed by taking the alloy chemistry into consideration. Apart from the intermetallic phases, the precipitation of a M 6 Ctype carbide phase within the matrix and the formation of near continuous films, comprising discrete M 6 C/M 23 C 6 carbide particles, at the austenite grain boundaries have been noticed in the alloy after prolonged service.

Influences of γ″ and δ Precipitations on the Microstructural Properties of 718 Alloy through HIP, Solid-Solution, and Different Aging Heat Treatments

“…Figure 6 shows the dimensions of 00 precipitations, which are increased with the extended soaking time, especially under higher temperature conditions (in the second step). Literature 22) pointed out that, at different aging treatments, the size of the 00 phase has a linear relationship with the cube root of soaking time. Therefore, the dimensions of 00 precipitations were increased (30.41 nm) after the 720 C 8 h, 620 C 4 h aging treatment (A8-4), which matches the results of extended soaking times resulting in increasing the weight percent of 00 precipitations as listed in Table 4.…”

Effect of Cr addition on γ–γ′ cobalt-based Co–Mo–Al–Ta class of superalloys: a combined experimental and computational study

“…As mentioned in earlier section, this is mainly due to increase in Ta partitioning to c 0 after Cr addition and thus also responsible for increase in stacking fault energy of c 0 precipitates. Cr do have an effect on increasing the yield strength of some nickel-based superalloys (such as Hastelloy, Alloy 625) due to the formation of Ni 2 (Cr, Mo) precipitates after prolonged aging [63,64]. Figure 5b shows a comparison of specific 0.2% proof stress values at 870°C for 10Cr2Ta/10Cr2Ta2Ti alloys with 2Ta/2Ta2Ti alloys, Co-Al-W-based and nickelbased MAR-M-247 alloy.…”

Fine Grains Forming Process, Mechanism of Fine Grain Formation and Properties of Superalloy 718

“…Thus, it can be inferred that the ¤ precipitates rotated to find another suitable habit plane variant parallel to the grain boundary. 23) Since the grains in a single-phase polycrystalline specimen generally have many different orientations, many different types of grain boundary are possible. 24) 3.2.2 Effect of compression strain on ¤ phase precipitation Cylindrical specimens with a diameter of 10 mm and a length of 15 mm were cold compressed to reductions of 0, 25, and 50%, respectively.…”