Evaluation of Powder-Processed Metals for Turbine Engine Ball Bearings

Abstract

Two different types of rolling element fatigue testers and a full-scale bearing tester were used in a program aimed at developing a highly fatigue-resistant powder-processed material (P/M) for use in turbine engine bearings. The testers were the single-ball machine evaluating 0.0238-m (15/16-in.)-diameter balls, a rolling contact fatigue machine evaluating 0.00953-m (⅜ in.) rods, and a full-scale bearing rig evaluating 140-mm-bore, 0.0238-m (15/16 in.)-diameter ball, angular contact thrust bearings. The two-element testers, used to screen three different P/M alloys and the baseline vacuum induction melted-vacuum arc remelted (VIMVAR) M-50 alloy, each produced essentially the same ranking for these materials. The best results, about twice the life of the baseline VIMVAR M-50, were achieved with P/M CRB-7, a 14 percent chrome corrosion-resistant alloy. P/M M-50 produced lives equivalent to VIMVAR M-50. P/M T-15, a 4 percent chrome alloy, exhibited lives ranging from that realized with the baseline material down to one third of that level. Based on these tests, CRB-7 was selected as the material out of which the balls and races for 20 full-scale 140-mm bearings were subsequently fabricated and tested. The tests were conducted at a thrust load of 34 872 N (7 840 lb) and at a speed of 12 500 rpm. A wear problem encountered in these tests was circumvented by nickel plating the cage guiding surfaces of the inner ring lands. The B10 rolling contact fatigue life realized with these bearings was equivalent to that expected for these same bearings had they been made of conventional VIMVAR M-50 material. These results were quite encouraging considering the fact that this was the first attempt at applying powder processing to the manufacture of aircraft-quality rolling element bearings.