Gunvant N. Maniar

Bio: Gunvant N. Maniar is an academic researcher from Carpenter Technology Corporation. The author has contributed to research in topics: Alloy & Superalloy. The author has an hindex of 8, co-authored 16 publications receiving 218 citations. Previous affiliations of Gunvant N. Maniar include Wilmington University.

Carbides in M-50 high speed steel

Abstract: The carbides in M-50 high speed tool steel were studied in detail. The dissolution of carbides as a function of austenitizing temperature, and their precipitation as a function of tempering temperature were characterized by X-ray diffraction and microchemical analysis. The carbides in the annealed steel are M23C6, M6C, M2C, and MC. Upon austenitizing, with increasing temperatures, the carbides dissolve in the order: M23C6, metastable M2C, M6C, and MC. The residual carbides in the heat treated steel are MC and stable M2C. The solvus temperatures of M23C6 and M6C were determined. Upon tempering the hardened steel, with increasing tempering temperatures, carbides precipitate in the order: M23C6, metastable M2C, MC, and M6C. It is shown that the composition of the precipitated metastable M2C is different from that of the residual stable M2C and it varies with the tempering temperature.

Effect of gamma-gamma prime mismatch, volume fraction gamma prime, and gamma prime morphology on elevated temperature properties of Ni, 20 Cr, 5.5 Mo, Ti, Al alloys

Abstract: This study was designed to provide a critical test for the postulate that the mismatch between the lattices of austenite (γ) and the age-hardening gamma-prime (γ′) precipitates and the resultant coherency strains have a significant influence on the elevated temperature, particularly stress rupture, properties of a nickel-base superalloy. Two experimental alloys with a base analysis of Ni, 20 Cr, 5.5 Mo were designed with variable titanium and aluminum additions. To discern the effect of mismatch, an alloy without molybdenum was also experimented with. By manipulating the mismatch and volume fraction γ′ by heat treatment and chemistry, it was shown that a lower γ-γ′ mismatch indeed is beneficial to stress rupture life. Importance of volume fraction γ′ on this elevated temperature was also established.

Heat treatment of 706 alloy for optimum 1200 °F stress-rupture properties

Abstract: Evaluation of a commercial heat treatment for 706 alloy indicated that it resulted in relatively low 1200° F stress rupture ductility. It was determined that this was caused by a solution treatment which dissolved all of the age-hardening phases in the alloy and caused a coarse grain size and supersaturated matrix condition. Based upon extensive fine structure study of the 706 alloy as well as previous experience with 718 alloy and other Fe−Ni-base superalloys, a heat treatment is developed which effectively optimizes the 1200°F stress-rupture properties of the alloy. The key to best properties was found to be the precipitation of globular to plate-like Ni3Cb/Ni3Ti at the grain boundaries in conjunction with maintaining a fine as-forged grain structure.

The microstructure of 706, a new Fe−Ni-base superalloy

Abstract: Alloy 706 is a precipitation-strengthened Fe−Ni-base superalloy which has been reported to have improved machining characteristics over other similar alloys. The present work was conducted to document the phase relationships of the alloy in comparison with other Fe−Ni-base alloys. The precipitated phases identified in the alloy include γ′, Ni3Cb, Ni3Ti, M23C6, and MC. A small amount of Laves phase was also detected. The effects of some composition variations on solvus relationships for γ′ and Ni3Cb/Ni3Ti are documented. Means to take advantage of the structural response of the alloy to develop desired properties are suggested. It is shown that on the basis of chemistry and microstructural response, 706 alloy can be considered to be intermediate to the well-known alloys, 718 and 901.

Morphology of y’ and y” precipitates and thermal stability of inconel 718 type alloys

Abstract: The precipitation of the γ’ (Ll2) and γ" (DO22) phases has been studied in four alloys Fe-Ni-Cr-Ti-Al-Nb containing a higher Ti + Al/Nb ratio than that of the INCONEL 718 alloy. For these alloys, the precipitation microstructure varies rapidly with aging temperature and composition. Bct γ"particles have always been found to precipitate on γ’ phase. Moreover, by aging three alloys above a critical temperature, a “compact ntorphology” has been observed: cube-shaped γ’ particles coated on their six faces with a shell of γ" precipitate. This microstructure has proved to be very stable on prolonged aging. A thermal stability better than that encountered in nominal INCONEL 718 alloy can thus be achieved. The influence of composition and aging temperature on the conditions that bring about this “compact morphology” has been investigated. A minimal Ti + Al/Nb ratio between 0.9 and 1 has been determined, allowing the “compact morphology” to be obtained.

Precipitation of the δ-Ni 3 Nb phase in two nickel base superalloys

Abstract: The precipitation of the equilibrium δ-Ni3Nb phase has been studied in two niobium bearing nickel base superalloys—INCONEL 718 and INCONEL* 625—both of which are hardenable by the precipitation of the metastableγ″-Ni3Nb phase. The morphology and the distribution of precipitates have been examined and the crystallographic orientation relationship between the austenite and theδ phases has been determined. The nucleation of theδ phase at stacking faults within pre-existing δ" precipitates has been discussed.

The role of alloying elements in the design of nickel-base superalloys

Abstract: The constituents of nickel-base superalloys have been classified into solid solution formers, precipitate formers, carbide formers and surface stabilizers. The characteristics of solutes which would make them most suitable in each category have been specified and appropriate alloying elements have been identified. Nickel-base superalloys are hardened primarily by the precipitation of Ni3X type compounds. The occurrence and crystallography of precipitation of various kinds of Ni3X type precipitates have been considered. The role of substitution by alloying elements on mismatch and stability of phases has been discussed. The free electron model and the Engel-Brewer model have been applied for evaluating the stabilities of precipitates, and the role of the alloying elements in determining the stabilities of external and internal surfaces such as grain boundaries have been briefly outlined.