Evolution behavior of δ phase in Cu12Sn2Ni alloy and the corresponding effects on alloy property

With the increase of tin content in tin bronze, the rise of δ phase made the strength, hardness of tin bronze increase and the ductility decrease sharply, that difficult to process. In this paper, the Cu12Sn2Ni alloy was prepared by centrifugal casting, the microstructure and phase formation before and after heat treatment were observed by x-ray diffraction, scanning electron microscope, and transmission electron microscope. The results showed that the as-cast sample microstructure was composed of equiaxed grains rather than coarse dendrites. centrifugal casting inhibits tin diffusion to form metastable phase β′-Cu_13.7Sn. The as-cast sample had good deformability and its tensile strength and elongation were 381.9 MPa and 12.4 %, respectively, which are higher than the mechanical properties of gravity casting. The tensile strength and elongation of the sample after furnace cooling at 620 °C/8 min are 439.5 MPa and 24.4 %, respectively, the increase was 16.6 % and 85.07 %, compared with the as-cast samples, due to the solid solution strengthening, the second phase strengthening and the homogenization of the microstructure.     

Effect of δ Phase on Hydrogen Embrittlement of Inconel 718 by Notch Tensile Tests

The effect of δ phase on the hydrogen embrittlement (HE) sensitivity of Inconel 718 was investigated by conducting notch tensile tests. Notch tensile specimens with various precipitation morphologies of δ phase were prepared with different heat treatments, and hydrogen was charged into the tensile specimens before tensile tests via a cathodic charging process. The loss of notch tensile strength (NTS) due to the charged hydrogen was used to evaluate the hydrogen embrittlement sensitivity. The results show that δ phase has deleterious effect on NTSs, and the fracture of hydrogen-charged specimens initiated near the notch surfaces. The loss of NTS caused by precharged hydrogen can be greatly decreased by dissolving δ phase. δ-free Inconel 718 alloy is proposed for the applications in hydrogen environments.     

The effect of δ alumina fibre arrays on the age-hardening characteristics of an Al-Mg-Si alloy

The effect of alumina fibre arrays on the age-hardening characteristics of an Al-Mg-Si alloy (6061) has been investigated by means of hardness and electrical resistivity measurements, and optical, scanning and transmission electron microscopy. It is shown that the fibre array can have a considerable effect on the age-hardening response of the matrix alloy in metal matrix composites, causing suppression of GP zone formation which inhibits natural ageing and considerably reduces the peak hardening produced during artificial ageing. The reduced hardening potential of the composites during artificial ageing is shown to result from a competition between GP zone formation and heterogeneous nucleation of the intermediate precipitate on lattice defects. The most probable cause of both phenomena is shown to be lack of quenched-in vacancies following solution treatment, due to the availability of a large number of vacancy sinks at the fibre-matrix interfaces.     

Deformation mechanisms in the γ-TiAl phase present in the Ti-46Al-2V-0.4Er alloy

Deformation microstructures of the -TiAl Phase in two-phase (₂ + ) alloy, Ti-46Al-2V-0.4Er (all compositions are given in atomic percent), have been studied by transmission electron microscopy. Heat treated samples of this alloy were subjected to 3% plastic strain in compression at room temperature, 600°C, and 900°C. Majority of dislocations present in the as heat treated and deformed samples are of b = 1/2 < 110] type. Formation of loops from the dislocations are also observed. Isolated super dislocations and faulted dipoles are seldom seen in the microstructures. Plenty of twins are present in these samples and it appears that their density increases with increasing deformation temperature. The deformation microstructures of the alloy studied here are quite similar to those in the binary two-phase titanium aluminides or the V containing two-phase titanium aluminides. It appears that Er does not significantly change the deformation microstructure of this two-phase alloy, although Er has a significant effect on the deformation microstructure of the single-phase -TiAl alloys.     

γ″Precipitate in Inconel 718

The γ"precipitate in Inconel 718 Ni-base superalloy has been investigated using TEM. Based on a calculation of diffraction pattern. the orientation relations between precipitates and matrix are given in detail. The influence of solution temperature on growth of γ" precipitates was investigated. and a γ" precipitate free area near δ phase was found. The coarsening behaviour of γ" precipitates during short time aging is discussed     

Isothermal decomposition of the ß′ phase in a Cu-Zn-Al alloy

The isothermal decomposition of theβ′ phase in a Cu-25 wt % Zn-6 wt % Al alloy was investigated using transmission electron microscopy and electron probe microanalysis. The ordering of theβ phase was too rapid to be suppressed during quenching from the solution annealing temperature. On ageing the alloy in the temperature range 603 to 703 K, theβ′ phase was found to decompose into a mixture of α+γ phases by the precipitation of fine and equiaxed γ-phase particles distributed uniformly throughout the matrix of α. The orientation relationship between α and γ was identified as $$\begin{gathered} (001)_\alpha ||(001)_\gamma \hfill \\ [010]_\alpha ||[010]_\gamma \hfill \\ \end{gathered} $$ The growth rate of the γ phase precipitates exhibited a maximum at 653 K. Electron probe microanalysis showed that the γ phase precipitates were enriched in aluminimum and depleted in zinc, compared to the α matrix. In addition to the uniform distribution of intragranular γ phase precipitates, heterogeneous precipitation of the α phase was observed along the grain boundaries indicative of a direct transformation ofβ′ to α in these regions: this reaction was found to be pronounced as the ageing temperature was increased up to 773 K.     

Deformation induced martensite characteristics in Fe–29Ni–2Mn alloy

Abstract

Deformation induced martensite characteristics in the austenite phase of Fe–29Ni–2Mn alloy were studied for different austenite grain sizes of alloy. Scanning electron microscopy, transmission electron microscopy, Mössbauer spectroscopy and also differential scanning calorimetry techniques were applied to study in order to clarify the deformation induced martensite characteristics from morphological, crystallographical, magnetical and thermal points of view. Scanning electron microscope revealed that the increasing of deformation amount also increased the amount of existed martensite. Transmission electron microscope observations showed that the crystal structure of these deformation induced martensites morphology was lenticular plates with a bcc crystal structure. Also the magnetism of both austenite and martensite phases were determined with Mössbauer spectroscopy. Mössbauer spectrometer measurements showed paramagnetic character for austenite phases and ferromagnetic character for martensite phases in all samples. According to obtained differential scanning calorimetry cooling curves, deformation induced martensite start temperature M _d was found to be higher (?128°C) for larger grained samples than for smaller grained samples (?135°C).     

Effect of Mo on the thermal stability of γ′ precipitate in Inconel 740 alloy

The effect of Mo on gamma prime (γ′) coarsening kinetics of Ni–25Cr–20Co–1.8Ti–0.9Al–2Nb–0.03C–xMo (x = 0.5, 3, 6 wt.%) alloys was investigated with respect to the activation energy for γ′ precipitate coarsening. The coarsening rates were measured at temperatures of 760 °C, 780 °C, and 810 °C up to 500 h. Coarsening rate decreased with increasing Mo, and the activation energies for coarsening were determined to be 245 kJ/mol, 261 kJ/mol, and 278 kJ/mol for 0.5 wt.% Mo, 3 wt.% Mo, and 6 wt.% Mo, respectively.     

Deformation behaviour of retained β phase inβ-eutectoid Ti-Cr alloys

Plastic deformation mode and its relation to tensile properties were investigated in retained phase of-eutectoid type Ti-Cr alloys. A plate-like single variant phase is induced during deformation of the most unstable phase having a minimum chromium content required to suppress martensitic transformation. A selected area electron diffraction pattern taken from a boundary region of the stress-induced phase plate can be explained by the idea that a single variant of phase is induced in a {3 3 2} 1 1 3 twin produced during deformation. Anisotropy in population of four phase variants decreases with increasing chromium content. On further increasing chromium content, deformation occurs by slip. Enhanced ductility is obtained in as-quenched Ti-Cr alloys accompanied by phase transformation or {332} 1 1 3 twinning during deformation, phase of as-quenched Ti-Cr alloys changes continuously from commensurate structure with sharp reflections to incommensurate structure with diffuse reflections with increasing chromium content. The obtained results in-eutectoid type Ti-Cr alloys are quite similar to those in-isomorphous type Ti-V alloys.     

Steady State Creep Rate Equation of Inconel 718 Superalloy

The steady state creep rate equdtion ofa nickel base superalloy Inconel 718, strengthenedby coherent ordered disc-shaped bct γ~(11) phaseand coherent spherical fcc γ~1 phase precipitates,has been established in the stress and temperatureranges of 620-840 MN m~(-2) and 853-943K, respecti-vely. Constant stress tensile creep tests wereused to medsure the values of steady state creeprate, ε_s, and the consecutive stress reductionmethod was used to measure the back stress duringcreep deformation. The values of effective stressexponent, n_e, were detemined from the slopesof the lgε_s vs. lg(σ_a-σ_0)/G plots. The effectof grain size, d, on steady state creep rdtehas been also studied in this investigation,and the grain size sensitive exponents m weredetemined from the slopes of lgε_s vs. lg(b/d)plots. The creep rate equations of Inconel 718,in the above stress and temperature ranges,have been proposed to beε_s=1.6×10~(-5)(D_1Gb/KT) (b/d )~(0.19)[(σ_a-σ_0)/G]~(1.35)in diffusional creep region, andε_s =75(D_1Gb/KT) (b/d)~(-0.42)[(σ_a-σ_0)/G]~(5.5)in dislocation power law creep region.     

Distinct dendritic α phase emerging on the surface of primary α phase in a compressed near-α titanium alloy

The characteristic of the surface morphology of primary α phase was studied in a deformed near-α titanium alloy. Dendritic α phase emerged on the surfaces of primary α phase when the alloy was air-cooled in α + β phase field after deformation. The dendritic α grain has the same orientation with its original primary α grain. The formation of the dendritic α phase could be explained by interface instability in epitaxial growth process of the primary α phase. The dislocations induced by deformation could facilitate the formation of dendritic α phase leading to the dendritic α phase and more obvious with the increase of strain. The growth of dendritic α phase was finally limited by the nucleation of second α phase with cooling.