A systematic investigation is made on the solid solution hardening of binary nickel alloys with additions of B-subgroup and transition metal elements. The 0.2% flow stress at 77 K and the Young's modulus are measured for a variety of binary alloys to evaluate the rate of solution hardening per one available data on the rate of change in lattice constant (da/dc), interpretation of the solution hardening that the hardening is more intense by the additions of transition metal elements than by the additions of B-subgroup elements where the hardening is linearly related with a combined parameter for the interaction between solute atoms and edge dislocations. Then the necessity is raised to carry out the similar type of investigation on the solution hardening of nickel in order to clarify whether the anomalous hardening effect is inherent in the Ll2 crystal structure of Ni3Al or in the majority component of nickel.Technological interest in nickel alloys has often centered on improving the heat resistant properties such as high temperature strength and creep strength by making alloys multicomponent. For this purpose, the additions of transition metals are generally accepted. Prominent examples are the modifications of commercial superalloys, in which the additions of those elements have been properly chosen utilizing regression analyses. As a more fundamental approach, the solid solution hardening has been studied in nickel binary alloys by a number of workers (2)- (9), however, the alloy

A systematic investigation is carried out on the temperature dependence of strength in ternary Ni3Al compounds with additions of transition metal elements. The rate of solid solution hardening per one with the rate of lattice parameter change, da/dc, although a linear correlation has been found for the addition of B-subgroup elements. The rate of change in activation energy to provide the anomalous positive temperature dependence of strength per one atomic percent of the solute, du/dc, is then evaluated. Together with the results for the addition of B-subgroup elements, the apparent valence is assigned for each transition metal element by an analogy utilizing equi-valence contour determined for B-subgroup elements. Then it becomes possible to discuss the relative magnitude of the mechanical anomaly in Ni3Al in terms of the phase stability concept of L12 phase, in which e/a ratio as well as the atomic radius ratio of the compound, RB/RA, as affected by ternary addition is an important parameter to alter the stability of the phase against other geometrically close packed phases. (Received August 9, 1985) Keywords shown that the characteristic mechanical anomaly of the compound is enhanced by such additions as to increase the electron-atom ratio and/or the atomic radius ratio of the compound. Then the rate of change in activation energy for the thermally activated process to provide the mechanical anomaly per one atomic percent of solute, dU/dc, has been evaluated for a variety of ternary alloying elements in relation to the valence difference between a ternary B-subgroup element andshown that the rate of solid solution hardening seems to be proportional to that of change in lattice parameter by additions of the Bsubgroup element, da/dc.In the present investigation, a similar strategy is extended toward evaluating the role of ternary additions of transition elements into the compound in its mechanical properties. Practically information on the effects of ter-

An attempt is made to interpret the solid solution hardening of Ni3Al alloys in terms of the elastic interaction between the strain fields of a dislocation and a solute. Ternary additions are made to the L12 intermetallic compound with both B-subgroup and transition metal elements which substitute for Al-sites. Young's modulus of the ternary alloys is measured and the rate of change in elastic constant per one atomic per cent of solute (dE/dc) is determined. With the available data for the rate of solution harden-

The object of this study is to investigate precipitation behavior during aging of age-hardenable Fe-Ni-Mn martensitic alloys by means of specific heat measurement , thermal differential analysis, electron microscopic observation, and X-ray and electron diffractions . The as-quenched structure before aging is lath martensite. In the initial stage of aging, very fine zones with high solute concentration are homogeneously formed due to the two-phase decomposition . Subsequently the zone acts as a nucleus of the fct NiMn phase. As the zone changes to the fct NiMn particle the hardness of the alloys increases up to its maximum value. The main cause of the age-hardening is considered to be the strain hardening due to the coherency strain between zone or NiMn particle and matrix . In the over-aging and softening processes, NiMn particles grow into disc-like platelets on the (100) planes of the matrix, and the crystallographic orientation relationship with respect to the matrix is determined and the structure is microduplex lamellae consisting of austenite and ferrite (or martensite) phases . The Kurdjumov-Sachs relationship holds between the austenite and ferrite.

A systematic evaluation has been made on the magnitude of the positive temperature dependence of strength in Ni3Al as affected by ternary additions of B-subgroup elements. The rate of change in activation energy to provide the mechanical anomaly per one atomic per cent of the solute, dU/dc, is determined for a variety of the ternary additions. It is shown that the larger the valence difference between the parameter change in the compound per one atomic percent of the solute, da/dc, the larger the dU/dC. These are well interpreted in terms of the phase stability concept to determine the relative magnitude of the mechanical anomaly in the Ll2 compounds, in which e/a ratio of the compound and the atomic radius ratio of the components, Re/RA, are the key factors to alter the stability of the phase against other geometrically close packed phases and thereby control the occurrence and the magnitude of the mechanical anomaly. The effect of ternary additions of B-subgroup elements on the rate of solid solution An intermetallic compound Ni3Al is one of the L12 compounds which show an anomalous positive temperature dependence of strength. The compound based on Ni3Al is a major microstructural constituent in commercial nickel base superalloys as precipitates to provide dispersion strengthening, and its volume fraction often reaches 60% or more. In alloy designing the superalloys for an improved high temperature performance, the best utilization of this compound is anticipated, which mechanical properties are known to be strongly affected by ternary alloy substitutions for one of or both of the components.In considering the effect of ternary additions on the mechanical properties of the compound Ni3Al, two factors are important, and they are the solid solution hardening and the magnitude of the positive temperature dependence of strength. Historically a work by Guard and Westbrook(1) was the first attempt on this regard in which the temperature dependence of hardness in Ni3Al as affected by various ternary additions was investigated. Recently the temperature dependence of 0.2% flow stress in Ni3Al with additions of several ternary alloying elements has been investigated by Thornton et a1.(2), Rawlings and StatonBevan(3) and Aoki and Izumi(4). There have been several reports(5)-(8) on the crystallographic orientation dependence of flow stress in single crystalline Ni3Al with small additions of Ti, Nb or W, but in those cases the alloy additions were made in order to suppress the peritectic reaction in the Ni-Al binary