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Microstructural evolutions of the 4Al alumina-forming austenitic steel after cold rolling with different reductions from 5% to 30% and then annealing were investigated using electron backscattering diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile properties and hardness were also measured. The results show that the average grain size gradually decreases with an increase in the cold-rolling reduction. The low angle grain boundaries (LAGBs) are dominant in the cold-rolled samples, but high angle grain boundaries (HAGBs) form in the annealed samples, indicating that the grains are refined under the action of dislocations. During cold rolling, high-density dislocations are initially introduced in the samples, which contributes to a large number of dislocations remaining after annealing. With the sustaining increase in cold-rolled deformation, the samples exhibit more excellent tensile strength and hardness due to the decrease in grain size and increase in dislocation density, especially for the samples subjected to 30% cold-rolling reduction. The contribution of dislocations on yield strength is more than 60%. [ABSTRACT FROM AUTHOR]

Alumina-forming austenitic (AFA) steel, a promising candidate for use in high-temperature components of ultra-supercritical power plants, has high creep strengths and outstanding high-temperature corrosion resistance. The effects of microstructural evolution on the mechanical properties of Fe-20Ni-14Cr-3Al alumina-forming austenitic (3Al-AFA) steel with micro-cold deformation were investigated by multiple characterization methods, and the micro-cold deformation process was analyzed by conducting compression experiments. Tensile properties and hardness were also examined. The results show that the reduction of deformation has significant influences on the increase in the density of dislocation, the reduction of grain size, and the distribution of precipitates, which play an essential role in the enhancement of mechanical properties. As the reduction of deformation increases, the density of dislocations rises, the fragmentation of grains results in a reduction of grain size, and the distribution of precipitates at the grain boundaries gradually increases, which causes a rise in strength and a decrease in elongation. Since the elastic deformation range expands with an increase in deformation before the strain reaches 5 ​% of the CR0 sample in the compression test, the variation in the average grain aspect ratio between a reduction of 2 ​% and 6 ​% is relatively small. It contributes more to hardness and strength when the grain aspect ratio is high. [ABSTRACT FROM AUTHOR]

Microstructural evolutions during hot deformation and annealing of alumina-forming austenitic (AFA) steel were investigated using electron backscatter diffraction (EBSD). Tensile properties of deformed and as-received AFA steels were also tested. The yield strength and ultimate tensile stress of deformed AFA steel increase gradually with the increase in rolling reduction, while the fracture elongation decreases rapidly. Specifically, after hot-rolling with the reduction of 40%, the yield strength of the annealed specimen is high to 773.2 MPa, and the fracture elongation of this sample is about 43.6%. The excellent mechanical properties can be attributed to the smaller average grain, larger Schmid factor and coincident site lattice (CSL) boundaries. Such a rapid decline of the elongation of AFA steel occurs due to increasing low angle grain boundaries (LAGB, <15°), the crystal defects and the degree of work hardening with the increase in rolling deformation. An approachable strategy to improve the tensile properties of annealed samples is to effectively hinder the dislocation motion during annealing at 700 °C when few LAGBs could transform into high angle grain boundaries (HAGB, >15°). [ABSTRACT FROM AUTHOR]

Abstract Microstructural evolution of modified 2.5Al alumina-forming austenitic steel after isothermal aging at 973 K was investigated by scanning electron microscope (SEM), and X-ray diffraction (XRD). Tensile and vicker's hardness tests were also carried out to study mechanical properties during isothermal aging. The average particle diameter of precipitates was statistically measured and the kinetic model was employed to describe the coarsening of precipitates. The results show that the precipitation sequence of Laves and NiAl phases was related to aging time, and precipitated after 20 h and 100 h in this work, respectively. The average particle diameter of precipitates continuously increased with aging time. And the coarsening rate of the precipitates decreased at 1000 h due to the exhaustion of Nb atoms in matrix. The precipitation of NiAl and Laves phases plays an important role in mechanical properties. The hardness and the work hardening rate continuously increased. In contrast, the elongation gradually decreased. The above results indicated that the effect of aging strengthening. The room-temperature yield strength firstly sluggish increased and then gradually decreased, finally increased significantly due to the increase in σ gb , the decrease in σ dis and σ ss , and the change in σ ppt. [ABSTRACT FROM AUTHOR]

The microstructural evolutions of the alumina-forming austenitic (AFA) steel subjected to different cold-rolled reductions and then aging at 700 °C were investigated by multiple characterization methods, and the mechanical properties were also examined. The results show that the increased dislocations (especially, edge dislocations) after cold rolling can effectively enhance the volume fraction and refine the particle size of precipitates during initial aging and subsequently accelerate the coarsening rate of precipitates in the AFA steel, resulting in a high coarsening exponent. The coarsening rate of B2–NiAl phase is higher than that of Laves phase. Excellent mechanical properties with a combination of yield strength (1152 ± 32 MPa) and elongation (44.8 ± 4.1%) of cold rolled AFA steel after aging for 2 h can be obtained due to co-strengthening contribution derived from dislocations and precipitates. With the duration of aging, the dislocation strengthening constantly decreases, the effect of precipitation strengthening is contrarily larger than that of dislocations. • The deformed dislocations evolved into high-density dislocation networks with the increase in cold-rolled reductions. • A large number of nano-scaled Laves phase and B2–NiAl phase precipitated around the dislocations during aging. • The coarsening rate of B2–NiAl phase was larger than that of Laves phase in the AFA steel. • The strengthening contribution from precipitates was larger than that from dislocations with the increase in aging time. [ABSTRACT FROM AUTHOR]

The stabilization of polyesteramide (PEA) was studied by TGA, melt index and intrinsic viscosity. Primary antioxidant A1010 (0.6 wt.%) combined with 0.2 wt.% of hydroperoxide decomposer A168 is effective in stabilizing PEA; but the holding life of PEA in the extruder barrel is only 30 min, and the antioxidants are completely consumed when it is extruded four times. Fillers including heavy calcium carbonate (HCC), tricalcium phosphate (TCP) and talc affect both the thermal stability and mechanical properties of the resultant composites, which are discussed in detail. The Turcsanyi model can best describe the composition dependence of tensile strength of the HCC and talc filled PEA, and the Sato-Furukawa can best predict the Young''s modulus of HCC filled PEA, but is poor for the talc-filled material [Copyright &y& Elsevier]

Alumina-forming austenitic (AFA) steel with great application potential in components of power plants has been developed due to its excellent high-temperature properties and corrosion resistance. Evolution of precipitates was characterized using multiple methods, and its effect on mechanical properties of Fe–20Ni–14Cr–3Al alumina-forming austenitic (3Al-AFA) steel after isothermal-aging at 973K was also assessed. The results showed that the particle size and volume fraction of precipitates (mainly Laves, B2–NiAl and σ phase) increase with the duration of isothermal-aging. The volume fraction of δ-ferrite increases significantly also with the extension of isothermal-aging time, which is regarded as a harmful factor to mechanical properties of AFA steel. The strength and Vickers hardness firstly increase and then decrease with the extension of isothermal-aging time, which is inversely proportional to the elongation at the initial stage of isothermal-aging. Both strength and elongation decrease with the isothermal-aging time between 500 h and 1000 h due to the δ-ferrite and coarse precipitates therein. Cr element firstly prone to segregate and diffuse in δ-ferrite, which promotes the diffusions of other alloying elements from matrix to δ-ferrite, resulting in the coarsening of precipitates in δ-ferrite region. The highest yield strength (1171 MPa) is achieved when the size of Laves and B2–NiAl precipitates in matrix is about 100–150 nm. [ABSTRACT FROM AUTHOR]

The effects of the relative content of Al and Ti, and the addition of 2 at.% Cr or Mo to partly substitute Co on the microstructure and mechanical properties of Co–Ni–Al–Ti superalloy were investigated. The microstructures of five as-cast superalloys showed that γ'-(Co,Ni) 3 (Al,Ti) precipitates segregated on γ-Co matrix and exhibited dendritic morphology. After aging, nano-sized γ'-(Co,Ni) 3 (Al,Ti) precipitates uniformly precipitated on γ-Co matrix. Ni, Al, Ti and Mo atoms partitioned preferentially to γ′ phase, while Co and Cr atoms partitioned preferentially to γ matrix phase. The increase in Ti content, and the addition of 2 at.% Cr or Mo all increased the volume fraction and the average size of γ′ phase. The lattice misfit increased with the concentration of Ti and the addition of 2 at.% Mo, but decreased with the addition of 2 at.% Cr. With increasing aging time, the size of γ′ phase and lattice misfit increased, while γ′ phase volume fraction increased firstly, and then decreased after reaching the maximum at 100 h. The lattice misfit plays a key role on vicker's hardness in the time of 20 h–100 h aging, while γ′ phase volume fraction plays a decisive role in vicker's hardness after 100 h aging. [ABSTRACT FROM AUTHOR]