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Thermal fatigue damage of high temperature titanium alloys and thermal fatigue crack growth (TFCG) behaviours are of great concern for severe temperature fluctuating environments. Cyclic thermal fatigue tests of heating to 700°C for 55 s followed by water cooling for 3 s at 20°C per cycle were performed with laser deposited Ti60A (Ti-5·54Al-3·38Sn-3·34Zr-0·37Mo-0·46Si) alloy. Thermal fatigue crack growth paths including crack length and crack growth directions were examined, as were their correlations with microstructure changes during the thermal fatigue process. Results show that local coarsened lamellar α developed by the interaction between cyclic thermal stress and oxygen atom interstitial solution effect occurs in the alloy after 800 cycles. Thermal fatigue cracks initiate after 800 cycles. Subsequently, total crack length increases with the volume fraction of local coarsened lamellar α from 800 to 2000 cycles. The enhanced oxygen penetration process plays a key role in the TFCG process. [ABSTRACT FROM AUTHOR]

Determining a damage period and the quantitative description of such are the subject matters of this paper. The refractory of magnesia-carbon was investigated by method of the unsubstantiated model detection system using the acoustic emission (AE) and the frequency-energy coupled analysis. Through consideration of the amplitude of the power spectrum and the characteristic frequency, the waveform overlap was resolved, and the damage was then separated into three periods. Furthermore, the centroid energy carried by the centric frequency was proposed in the explanation of a sophisticated microstructure proposition. According to the centroid energy, the damage factor d was utilized in the construction of the constitutive equations. Through numerical estimation, the numerical results indicate that the introduction of the damage factor d as the input parameter for the constitutive equation is practical. [ABSTRACT FROM AUTHOR]

A novel process of manufacturing high performance AZ31 alloy strip was put forward by combining semisolid rolling, deep rolling and heat treatment, and the effects of dynamic recrystallisation during deep rolling of semisolid slab and heat treatment on microstructure and properties of AZ31 alloy were investigated. When the casting temperature was set from 650 to 690uC and the vibration frequency was controlled at 80 Hz, AZ31 alloy strip with the cross-section size of 46160 mm and fine near round and rosette grains was manufactured by semisolid rolling. Dynamic recrystallisation happened during deep rolling process. Dynamic recrystallisation grain size decreases with the increase in deep rolling temperature in a certain scope. With the increase in deep rolling deformation amount, the microstructure evolved gradually from coarse primary grains and twins to fine dynamic recrystallisation grains and twist primary grains as well as small regular equiaxed grains. AZ31 alloy strip with very fine equiaxed grain in size of 6 mm was obtained by deep rolling. After solution treatment at 415°C for 20 h, the saturated solid solution of AZ31 alloy strip has been formed. After solution treatment at 415°C for 20 h and aging at 230°C for 16 h, the deep rolled AZ31 alloy strips exhibit excellent mechanical properties; the ultimate tensile strength, yield strength, elongation to failure and hardness could reach 330 MPa, 204 MPa, 11% and 71 HV respectively. [ABSTRACT FROM AUTHOR]

In the backward slip zone, the buckling direction of the isothermal lines near the surface of the alloy was toward the exit of the roll gap, the buckling direction of the isothermal lines at the centre was toward the entrance of the roll gap and semisolid metal deformation happened. In the forward slip zone, the buckling direction of the isothermal lines was toward the exit of the gap, the bending degree increased from the neutral flow plane to the exit of the roll gap and solid metal deformation took place. The microstructure of the strip became more refined with the decrease in casting temperature. When the casting temperature was between 670 and 690°C and the rolling speed was 0·167 m s-1, the alloy AZ31 strip with cross-section size of 4×160 mm was prepared. The mechanical properties of the product were higher than that of conventional roll casting. [ABSTRACT FROM AUTHOR]

Microstructure evolution during a novel rheorolling process for producing A356 alloy strip was investigated. Under the high cooling rate caused by the sloping plate and stirring action caused by the vibration and metal flow, high nucleation rate and dendrite breakage happened during the process, which causes the formation of fine spherical or rosette primary grains. The grain size of the primary α.-Al phase decreased with the decrease in casting temperature in the cooling slope, but the volume fraction of the primary α-Al phase increased. The change of the primary grain shape is not obvious in the roll gap during the rolling process, and most of the primary grains nearly kept round or rosette shapes. When the casting temperature is 660°C, the strip with a cross-section of 4×160 mm was produced, and homogeneous microstructure was obtained. [ABSTRACT FROM AUTHOR]

In the present work, the effects of Zn content on the microstructures and mechanical properties of as cast Mg-xZn-5Y-0·6Zr alloys (x52, 5, 8 and 13 wt-%) have been investigated. The results show that the ternary Mg-Zn-Y phase compositions change with Zn/Y ratios induced by the change in Zn content. It is found that the fracture is mainly decided by the characteristics and distribution of second phase rather than the grain size. The influences of these phases, especially the W phase, on the mechanical properties of the alloys have been discussed. Both ultimate tensile strength (UTS) and elongation decrease with the increase in Zn content, while the instance of yield strength (YS) is just the reverse. The W phase is easily cracked because of its brittleness and easy to result in decohesion from the matrix because of the weak atomic bonding, which greatly degrade the UTS and elongation. It can be concluded that the YS closely depends on the grain size, while UTS and elongation closely depend on the volume fraction of eutectic compound (a-MgzW phase). [ABSTRACT FROM AUTHOR]

The effects of yttrium (0, 2·5, 4·0 and 6·0 wt-%) on the microstructures, age hardening behaviours and mechanical properties of the Mg-2·4Nd-0·2Zn-0·4Zr alloys were investigated. The results demonstrated that the Mg-2·4Nd-0·2Zn-0·4Zr alloy was mainly composed of α-Mg and Mg12Nd phases. When Y was the added into Mg-2·4Nd-0·2Zn-0·4Zr alloy, Mg24Y5 phases formed. The volume fraction of Mg24Y5 phases increased, and the grains were refined with the Y element increasing. Moreover, the additions of Y could improve the peak aged hardness and mechanical properties of the alloys. Mg-2·4Nd-0·2Zn-0·4Zr-6Y alloy exhibited the highest yield strength of 280 MPa in 225uC peak aged condition; Mg-2·4Nd-0·2Zn-0·4Zr-4·0Y alloy exhibited the optimal mechanical properties in the peak aged condition, whose value of ultimate tensile strength, yield strength and elongation were 330 MPa, 265 MPa and 6·5% respectively. The optimal mechanical properties of Mg-2·4Nd-0·2Zn-0·4Zr-4·0Y alloy were mainly attributed to the high volume fraction of fine metastable β' precipitates in the matrix and the discontinuous distribution of the sparse grain boundary precipitates along grain boundary. [ABSTRACT FROM AUTHOR]

A sloping semisolid rheorolling process of AZ91 alloy was developed, and the effects of process parameters on microstructure and properties of AZ91 alloy strip prepared by the proposed process were investigated. The grain size and roundness of the strip increase with the increment of casting temperature, and the ultimate tensile strength and elongation of the strip decrease. The primary grain size increases with the increment of roll speed. The grain size of the strip decreases first and then increases with the increment of vibration frequency, and mechanical properties increase first and then decrease. When the casting temperature was between 670 and 690°C, the roll speed was 0·052 m s-1, the vibration frequency was 80 Hz, the amplitude was 0·55 mm and the sloping angle was 45°, the AZ91 alloy strip was produced. The ultimate tensile strength of the strip is 215 MPa, and the elongation is 3·02%. [ABSTRACT FROM AUTHOR]

Nitrogen-doped SrTiO3 samples have been successfully prepared by nitrogen-ion implantation. X-ray photoelectron spectra clearly indicate the presence of nitrogen dopants in the crystal lattice of SrTiO3. The ultraviolet–visible absorption spectra of nitrogen-doped SrTiO3 show enhanced visible light absorption in the range of 400–500 nm, which contributs to the localized N 2p state in the band gap of SrTiO3. The resistance coefficient of temperature is positive indicating metallic conducting behavior. The nonlinear dependence of voltage on current at liquid-nitrogen temperatures indicates a possible energy barrier in the grain boundary.PACS Nos.: 72.20.–i, 72.80.Ga, 78.20.–e [ABSTRACT FROM AUTHOR]

Co-doped SnO2 nanoparticles were synthesized by a simple hydrothermal method, and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM), UV–Vis diffuse reflectance spectra (DRS) and Photoluminescence spectroscopy (PL). It is found that the SnO2 crystallites with the tetragonal rutile structure formed directly during the hydrothermal process without calcination. The Co-doped SnO2 nanoparticles were spheric and well-dispersed with narrow size distribution. The crystalline size of SnO2 decreased from 5.98 to 2.22 nm when the Co content increased from 0% to 20%. A considerable red shift in the absorbing band edge was observed with increasing of Co dopant. [ABSTRACT FROM AUTHOR]

The rare earth element cerium (Ce) was added to cast binary Ti-44 at.% Al alloys by arc melting in the range of 0.05 to 0.3 atomic percent. It was observed that the as-cast structures of the ingots consisted of the usual three zones of fine equiaxed grains near the mould wall, columnar grains growing away from the mould wall and coarse equiaxed grains near the center. Ce greatly promoted the growth of columnar grains and reduced their diameters. The ingots were subsequently heat treated to obtain well-defined fully lamellar structures. The material containing no rare earth displayed large equiaxed lamellar colonies of average size of >1400 μm; the material with 0.05 at.% addition of Ce consisted of lamellar colonies of as fine as ∼440 μm. The finest grain size of this material was 320 μm at the top position in the ingot. [ABSTRACT FROM AUTHOR]