Effect of heat treatment on microstructures and mechanical properties in a full lamellar PM TiAl alloy
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The effect of heat treatment on the microstructures and tensile properties of a powder metallurgical (PM) TiAl based alloy has been investigated in this paper. The near gamma (NG) microstructure is transformed to a full lamellar (FL) microstructure with an average grain size of 100 μm by heat treatments. The lamellar spacing of FL structure decreases with the increase of cooling rate. For cooling rates of 5, 10 and 50 °C/min, the lamellar spacing is 1.9, 1.0 and 0.8 μm respectively. The room temperature tensile properties exhibit an increasing trend with decrease of lamellar spacing.Isothermal process
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Some characteristic microstructures of Ti-6Al-4V, including lamellar microstructure, bimodal microstructure and equiaxed microstructure have been intensively investigated in the last 30 years. Nevertheless, the bi-lamellar microstructure, which was first defined by G. Lutjering, has not attracted much attention, despite of its significant benefits on various mechanical properties. In the present study, the fine secondary α lamellars (∼300nm) in the basketweave form, which are so-called bi-lamellar microstructure, were obtained in-between coarse α lamellars after intercritical annealing treatment in α + β region. The effects of intercritical annealing temperature (800∼960°C) and cooling rate (water quench∼100°C/min) on the bi-lamellar microstructure as well as its tensile strength at room temperature were systematically studied. The phenomenon of peak yield/tensile strength at 880°C was found for the first time and possible reasons for it were briefly discussed based on TEM observations after tensile deformation.
Equiaxed crystals
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Elongation
Titanium alloy
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Abstract By alloy melting, microstructure analysis and micro-hardness test, the effects of Sm addition on the microstructure of Mg-12Gd-2Y-0.5Zr alloy with solution treatment and aging treatment were investigated. The results showed that the microstructure of the tested alloy consisted of α-Mg matrix, Mg 41 Sm 5 , Mg 5 Gdm, Mg 24 Y 5 and β’ phases, and Sm improved the micro-hardness value of α-Mg matrix attributed to its better solid solution strengthening effect in α-Mg. The micro-hardness of the alloy with Sm increases obviously from HV121.4 to HV134.3 when compared with that of Mg-12Gd-2Y-0.5Zr alloy.
Matrix (chemical analysis)
Vickers hardness test
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Cu–10% P–6% Sn alloy rods with columnar crystal structure were synthesized in this study utilizing Cu–10% P–6% Sn alloy as the starting material. Continuous directional solidification was used to produce Cu–10% P–6% Sn (mass percentage) alloy rods with a diameter of 8 mm, and the heat treatment procedure was arried out under the condition of cast alloy. Optical microscopy and field emission scanning microscopy were then used to investigate the microstructure of the cast alloy. The impact of heat treatment on microstructure evolution was also investigated. The microstructure of a Cu–10% P–6% Sn alloy produced by continuous directed solidification had a Cu-rich dendritic structure, and the second phase structure was linear or spherical, according to the findings.
Rod
Directional solidification
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A review was given for progress in the research of the microstructure and characterization method of thermally sprayed coatings. Thus the characteristics of pores, the measurement of the pore rate, and the method to characterize the pores of the thermally sprayed coatings were highlighted, while the research on the lamellar structure and inter-lamellar bonding of the thermally sprayed coatings was briefed. It was pointed out that the pores in the thermally sprayed coatings were dominated by two-dimensional structure. Therefore it would be imperative to take into account both the porosity rate and the lamellar microstructure in the investigation of the microstructure of the thermally sprayed coatings.
Characterization
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Abstract The effect of Sr addition on the microstructure of a melt-spun Al-12% Si alloy has been investigated using X-ray diffraction and transmission electron microscopy. The Sr addition has no effect on the phase constitution but has a marked effect on the microstructure of the melt-spun alloy. The distribution, morphology and orientation of Si in the melt-spun alloy with the Sr addition are different from those in the alloy without Sr. Under rapid solidification conditions, cooling rates play a dominant role in the microstructure formation of the Al-12% Si alloy.
Melt spinning
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The fine fully lamellar (FFL) microstructure and intermedium microstructures in the process of forming FFL microstructure were examined under optical and transmission electronic microscopes. Based on the observation results, the transformation mechanism of FFL microstructure was analyzed and proposed as that the fine γ/α lamellar colonies form at the high temperature in the α single phase region through the precipitating of the α plates on the four equivalent habit planes {111}γ, in each γ matrix grain and then evolve to the γ/α2 lamellar colonies of the FFL microstructure.
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Equiaxed crystals
Volume fraction
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A new type of microstructure,named bi-lamellar microstructure of titanium alloy comes out of precipitated small secondary α needles in the β matrix through modification heat treatment.A comparison of microstructure and property of titanium alloy between equaixed,bi-model and lamellar microstructure is made.The results manifest that bi-lamellar microstructure improves the fracture toughness and fatigue crack propagation behavior of TA15 alloys remarkably,increases the length of fatigue crack propagation and brings about large secondary cracks.
Titanium alloy
Titanium aluminide
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