The application of friction stir processing (FSP) to a cast NiAl bronze (NAB) material is presented as a means for selective modification of the near-surface layers by converting as-cast microstructures to a wrought condition in the absence of macroscopic shape change. This may enable selective surface hardening of cast components. The complex physical metallurgy of the NAB is reviewed, and microstructure changes associated with FSP for a selected set of processing parameters are examined by optical microscopy (OM) and transmission electron microscopy (TEM) methods. Direct temperature measurement in the stir zone is infeasible and, so, these microstructure changes are used to estimate peak temperatures in the stir zone. The persistence of a Fe3Al phase (κii) indicates that peak temperatures are below the solvus for this phase, while the presence of transformation products of the β phase, including fine Widmanstatten α, bainite, and martensite, indicates that peak temperatures exceed the eutectoid temperature for the reaction β → α+κiii throughout the stir zone.

Microstructural modification of as-cast NiAl bronze by friction stir processing

Application of the divorced eutectoid transformation to the development of fine-grained, spheroidized structures in ultrahigh carbon steels

L'ecoulement plastique des solides polycristallins a lieu par l'un des trois mecanismes independants de deformation: glissement des dislocations, glissement des joints de grains, et flux diffusionnel directionnel. Developpement des equations constitutives decrivant chacun des trois mecanismes. Les equations se fondent sur une dependance exponentielle de la vitesse de deformation. Determination de l'exposant de contrainte. Influence de la microstructure: taille des grains, taille des sous-grains, densite des dislocations. Description quantitative des competitions entre ces differents mecanismes. Analyse du processus dominant

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On constitutive equations for various diffusion-controlled creep mechanisms

Ultrahigh carbon (UHC) steels have been investigated for their strength and ductility characteristics from 600 to 850°C. It has been shown that such UHC steels, in the carbon range 1.3 to 1.9 pct C, are superplastic when the microstructure consisted of fine equiaxed ferrite or austenite grains (∼1 μm) stabilized by fine spheroidized cementite particles. The flow stress-strain-rate relations obtained at various temperatures can be quantitatively described by the additive contributions of grain boundary (superplastic) creep and slip (lattice diffusion controlled) creep. It is predicted that superplastic characteristics should be observed at normal forming rates for the UHC steels if the grain size can be stabilized at 0.4 μm. The UHC steels were found to be readily rolled or forged at high strain-rates in the warm and hot range of temperatures even in the as-cast, coarse grained, condition.

Mechanical behavior of superplastic ultrahigh carbon steels at elevated temperature

An ultrahigh carbon (UHC) steel/mild steel laminated composite and a UHC steel/UHC steel laminate have been successfully manufactured by a roll-bonding procedure. Impact properties of these laminates, as well as of monolithic samples of the steels contained in these laminates, have been determined in the crackarrestor orientation over the temperature range 25 to −196°C. Both notched and unnotched samples of the laminated composite and laminate have been tested. Extremely low ductile-to-brittle temperatures of −140°C, and very high shelf energies (>325 J), have been found both for the laminated composites and the laminates. This remarkably good behavior is shown to be a result of notch blunting by delamination within the laminates.

The impact properties of laminated composites containing ultrahigh carbon (UHC) steels

Superplastic ultra high carbon steel

: EL 304, STRAIN RATEThe deformation of AISI type 304 austenitic stainless steel, Mangalloy (Fe-14% Mn-3%Ni), E-Brite 26-1 (Fe-26%Cr-1%Mo) ferritic stainless steel, 1018 steel containing 0.5%W, and 7075 aluminum has been studied in torsion over a range of deformation conditions representative of 'warm working' (0.4-0.6Tm, where Tm is the melting temperature of the alloy at strain rates from 0.01/s to 6.3/s). The results obtained at the various temperatures and strain rates were analyzed taking into account atom diffusivity and elastic modulus plotting the data as diffusion compensated strain rate versus the modulus compensated stress for each alloy. A clear separation in strength characteristics between the various alloys was obtained when the contribution from dislocation pipe diffusion was included in the diffusion coefficient indicating that diffusion along dislocations is important during warm working. (Author Modified Abstract)

Eldon M. Cady

Papers

Superplastic ultra high carbon steel

Studies on the Warm Working Characteristics of Alloys.