EFFECTS OF MELTING PRACTICE AND ALUMINUM COATING ON THE LIFE OF GMR 235 BUCKETS OPERATED ATn1650° F IN A TURBOJET ENGINE

摘要

The evaluation of the GMR 235 buckets was made in a J33-9 engine operating under cyclic conditions. A single cycle consisted of a J.5minute rated-speed (11,500 rpm) interval followed by an approximate 5minute idle-speed (4000 rpm) interval. The investigation indicated that vacuum-melted buckets had better than twice the life of air-melted buckets when life was based on time to fracture. However, there did not appear to be an appreciable difference between vacuum-melted or air-melted buckets when performance was based on time to cracking of the buckets by thermal fatigue. Aluminum coating appeared to improve the resistance to thermal fatigue and the time to fracture of the air-melted buckets;however, other factors present in the fabrication and testing of these buckets may have contributed to their apparent better performance. The improvements thus could not be attributed to aluminizing alone. Aging of air-melted buckets did not significantly affect performance with respect to crack formation or time to fracture. Diffusion heat treatment alone slightly decreased the thermal-fatigue resistance of vacuum-melted and air-melted buckets but increased slightly the time to fracture of air melted buckets.