Jiangbo Sha

EFFECT OF VACUUM INDUCTION MELTING TECHNOLOGY ON MECHANICAL PROPERTIES OF Nb-16Si-22Ti-2Al-2Hf-17Cr ALLOY

This paper dealt with the effect of different induction melting technologies on mechanical properties of Nb-16Si-22Ti-2Al-2Hf-17Cr alloy. The cast ingots were fabricated first by arc-melting, and then remolten in the vacuum induction furnace. The results showed that the ingot with refining process of 1800°C/15min and 0.1 at% C addition had finer microstructure and higher room-temperature fracture toughness. In addition, the compressive strength of the ingot with refining technology of 1700°C/10min was 315MPa at 1250°C. However, the arc melting ingot had the lowest fracture toughness and high-temperature compressive strength.

Dependence on temperature of tensile properties of the single-crystal superalloy DD11

ABSTRACT Tensile tests within a temperature range from room temperature (RT) to 1100°C were performed on a novel second-generation single-crystal superalloy DD11. The experimental results indicated that the yield strength (YS) remained constant up to 760°C, while a maximum was reached at 850°C. The elongation and area reduction decreased gradually from RT to 760°C and then they increased rapidly at temperatures above 760°C. As for the deformation mechanism, when the temperature was below 850°C, the γ′ precipitates were sheared by isolated faults, faulted loops and dislocation pairs. The formation of dislocation networks and dislocation climb mechanism were confirmed at temperatures above 980°C. Finally, the relationship between the YS of the DD11 alloy and the operative deformation mechanism was discussed.

EFFECTS OF COOLING RATE AND POURING TEMPERATURE ON MICROSTRUCTURE AND FRACTURE TOUGHNESS OF THE INDUCTION MELTED Nb-16Si-22Ti-2Hf-2Cr-2Al ALLOY

The effects of cooling rate and pouring temperature on microstructure and fracture toughness of the induction melted Nb-16Si-22Ti-2Hf-2Cr-2Al alloy were extensively investigated. The results revealed that with the decrease of cooling rates, the Nbss exhibits the dendrite-like morphology, the primary Nb5Si3 blocks form and the mean sizes of Nb5Si3, Nbss and eutectic colonies increase; with the increase of the pouring temperature, the microstructure shows columnar structure and the particles of Nb5Si3 or Nbss become long and thin. Pouring temperature and cooling rate had little influence on the volume fractions of Nbss and Nb5Si3 and their compositions. The Nb3Si phase eliminated in the case of high pouring temperature and slow cooling rate. Fracture toughness of the alloy prepared by induction melting is on the order of 13.7 to 15.3 MPa·m1/2. Similar fracture toughness value of each slab may be ascribes to the same volume fraction of the Nbss.