Seiya Furuta

PM nickel-base superalloy dual-property disks produced by superplastic forging

Abstract A manufacturing process for dual-structured turbine disks made from PM nickel-base superalloys has been specially developed. The disks are composed of two metals: AF115, which has superior stress rupture properties, was used in the rim region, and TMP-3, which has good tensile properties and a low cycle-fatigue life, was used in the bore region. A 400mm diameter dual-property disk was successfully produced through double-stepped HIP treatment and superplastic forging, in which gas atomized powders composed of the above alloys were consolidated into a well-designed preformed structure. After heat treatment, the microstructure of the product was very fine and homogeneous in the bore region, and coarse grains were obtained in the rim region. The mechanical properties were of such high quality as to enable practical use as a turbine disk.

The Relationship between Fatigue Crack Propagation Property and Fatigue Life at Elevated Temperatures on P/M Ni-base Superalloy, AF 115. Through Fatigue and Creep Strain Energy Parameters, .DELTA.Wf and .DELTA.Wc.

Low cycle fatigue properties under pure fatigue and creep/fatigue conditions were evaluated using a powder metallurgy superalloy, AF 115, containing a variety of defect-types and defect-sizes. The relationship between life, defect size, and loading condition were analyzed on the basis of crack growth rules and strain energy parameters. Following results were obtained ; (1) Inclusions, micro porosities and prior particle boundaries were observed at the origin of fatigue specimens. (2) By treating these defects as either cracks or notches, the lower or upper boundary of fatigue life can be obtained from the elastic-plastic strain energy parameter, lWf, and the fatigue crack growth rule. (3) The introduction of a tension hold period to the stress cycle or a decrease in the strain rate in the strain cycle significantly affects the fatigue life. The linear summation rule for partitioned lives, based on the elastic-plastic and creep strain energy parameters, lWf and lWc, and fatigue and creep crack growth rules, is suitable for life estimation under creep/fatigue conditions.

Properties of Ni-base Superalloy Powders Produced by Ar Gas Atomization

The fatigue properties of P/M superalloys can be significantly damaged by defects, which act as sites for fatigue fracture initiation. These defects can be introduced as inclusions either during the melting operation, during powder atomization or during subsequent handling.Equipments for producing cleaner powders by Ar gas atomization have been designed and installed, and the properties of produced MERL76 superalloy powders were examined. As a result, this method was capable of producing fine and clean powders with an average grain size of 56 μm and an oxygen content of less than 100 ppm. Results also indicated that the amount of non-metallic inclusions of produced powders was less than those in the commercialized powders, which was detected by the new water elutriation method.

Mechanical Properties of High Carbon Adamite P/M Steels

Five compositions of high carbon adamite steel powders (1.8%C, 2.2%C, 2.6%C, 2.9%C, and 3.7%C+1. 2%Ni+1.2%Cr+0.3%Mo) were produced by gas-atomization, and their fully densified P/M steel billets were made by hot isostatic pressing. Microstructures and mechanical properties of the P/M steels were investigated in comparison with the conventional adamite steel (1.7%C+l.2%Ni+l.2%Cr+0.3%Mo).In the P/M steels, fine carbides are uniformly distributed, whereas in the conventional steel, large-sized carbides are distributed among fine carbides.Mechanical properties of the P/M steels are as follows: The wear property of the P/M steels is improved with the increase of carbon content. On the contrary, the bend strength and fire cracking properties are decreased with increasing carbon content. But, these properties of the 2.5%C adamite P/M steel are found to be superior or equivalent to those of the conventional steel.