Yuyong Chen

Influence of Voids on the Tensile Performance of Carbon/epoxy Fabric Laminates

Abstract This paper aims at investigating the effect of voids on the tensile properties of [(±45) 4 /(0,90)/(±45) 2 ] s and [(±45)/0 4 /(±45)(0,90)] s composites. Specimens with void contents in the range of 0.4% to 9.0% were fabricated from carbon/epoxy fabric. The void content was determined by ultrasonic attenuation and optical image analysis, and microscopic inspection was also used to analyze the shape and size of the voids. The influence of voids on the tensile strength and modulus of both stacking sequence is compared in terms of the size and the shape of the voids. The effect of voids on the initiation and propagation of tensile failure of both stacking sequence composite was investigated.

Influence of voids on interlaminar shear strength of carbon/epoxy fabric laminates

Abstract The effects of voids (void content, void shape and size) on the interlaminar shear strength of [(±45) 4 /(0,90)/(±45) 2 ] S and [(±45)/0 4 /(0,90)/0 2 ] S composite laminates were investigated. Specimens with void contents in the range of 0.2%–8.0% for [(±45) 4 /(0,90)/(±45) 2 ] S and 0.2%–6.1% for [(±45)/0 4 /(0,90)/0 2 ] S were fabricated from carbon/epoxy fabric through varying autoclave pressures. The characteristics of the voids were studied by using optical image analysis to explain the interlaminar shear strength results. The influences of voids on the interlaminar shear strength of the two stacking sequences were compared in terms of the void content and size and shape of the void. The effect of voids on the initiation and propagation of interlaminar failure of both stacking sequence composites was found.

Microstructures and properties of titanium alloys Ti-Mo for dental use

Abstract The microstructures and properties of a series of binary Ti-Mo alloys with molybdenum contents ranging from 5% to 20%(mass fraction) were investigated. The experimental results indicate that the crystal structure and morphology of the cast alloys are sensitive to their molybdenum contents. When the Mo content is 5%, the equiaxed α crystal grain is observed. When the Mo content is 10%, the equiaxed α crystal grain and fine needles β phase are observed. When the Mo contents are 15% and 20%, only the equiaxed β crystal grain is observed. When the Mo content is 10%, the synthetical properties of the Ti-Mo alloy are the best. The data of hardness (HV451), compression strength (1636 MPa), compression ratio (22.5%) and elastic modulus (29.8 GPa) were collected. The increase of molybdenum contents is propitious to crystal refinement and improvement of plasticity of Ti-Mo alloys. The dry wear resistance of Ti-Mo alloys against Gr15 ball was investigated on CJS111A ball-disk wear instrument. The results show that the dry wear resistance of Ti-Mo alloys is correlative with hardness and mechanical properties. With the ductility increasing, the dry wear resistance reduces. The friction coefficient of 10%Mo alloy is the lowest, the dry wear resistance is the best. The wear particles, wear scar depth and width of the 10%Mo alloy are smaller than that of other Ti-Mo alloys. Considering all kinds of properties of Ti-Mo alloys, 10%Mo alloy is prospective dental prostheses material.

Microstructures and mechanical properties of TiAl alloy prepared by spark plasma sintering

Abstract A fine-grained TiAl alloy with a composition of Ti-47%Al(mole fraction) was prepared by double mechanical milling(DMM) and spark plasma sintering(SPS). The relationship among sintering temperature, microstructure and mechanical properties of Ti-47%Al alloy was studied by X-ray diffractometry(XRD), scanning electron microscopy(SEM) and mechanical testing. The results show that the morphology of double mechanical milling powder is regular with size of 20−40 μm. The main phase TiAl and few phases Ti 3 Al and Ti 2 Al were observed in the SPS bulk samples. For samples sintered at 1000 °C, the equiaxed crystal grain was achieved with size of 100−250 nm. The samples exhibited compressive and bending properties at room temperature with compressive strength of 2013 MPa, compression ratio of 4.6% and bending strength of 896 MPa. For samples sintered at 1100 °C, the size of equiaxed crystal grain was obviously increased. The SPS bulk samples exhibited uniform microstructures, with equiaxed TiAl phase and lamellar Ti 3 Al phase were observed. The samples exhibited compressive and bending properties at room temperature with compressive strength of 1990 MPa, compression ratio of 6.0% and bending strength of 705 MPa. The micro-hardness of the SPS bulk samples sintered at 1000 °C is obviously higher than that of the samples sintered at 1100 °C. The compression fracture mode of the SPS TiAl alloy samples is intergranular fracture and the bending fracture mode of the SPS TiAl alloy samples is intergranular rupture and cleavage fracture.

Microstructure, mechanical properties and dry wear resistance of β-type Ti–15Mo–xNb alloys for biomedical applications

Abstract In order to study the effect of element Nb on the microstructure and properties of the biomedical β -type Ti-Mo based alloys, Ti-15Mo- x Nb ( x =5, 10, 15 and 20 in %) alloys were investigated. The dry wear resistance of β -type Ti-15Mo- x Nb alloys against Gr15 ball was investigated on CJS111A ball-disk wear instrument. Experimental results indicate that crystal structure and morphology of the Ti-15Mo- x Nb alloys are sensitive to their Nb contents. Ti-15Mo- x Nb alloys match those for β phase peaks and no any phases are found. The Vickers hardness values of all the Ti-15Mo- x Nb alloys are higher than HV200. The compression yield strength of the Ti-15Mo-5Nb alloy is the lowest and that of the Ti-15Mo-10Nb alloy is the highest. For all the Ti-15Mo- x Nb alloys, the friction coefficient is not constant but takes a higher value. In dry condition, SEM study reveals deep parallel scars on the wear surfaces of all the Ti-15Mo- x Nb alloys under different loads. The friction coefficient of the Ti-15Mo-5Nb alloy under 1 N is the lowest. The wear principal mechanism for Ti-15Mo- x Nb alloys is adhesive wear.

Effects of minor yttrium addition on hot deformability of lamellar Ti-45Al-5Nb alloy

Abstract The effects of 0.3%(molar fraction, the same below) yttrium addition on hot deformability of lamellar Ti-45Al-5Nb alloy were investigated by simulated isothermal forging tests. The ingots with the nominal compositions of Ti-45Al-5Nb and Ti-45Al-5Nb-0.3Y were prepared by induction skull melting. Simulated isothermal forging tests were conducted on Gleeble 1500D thermo-simulation machine using a 6 mm in diameter and 10 mm in length compressive specimen at the deformation temperatures of 1 100, 1 150, 1 200 °C and strain rates of 1.0, 0.1, 0.01 s −1 . The results show that yttrium addition remarkably improves hot deformability of Ti-45Al-5Nb alloy. An appropriate hot deformation processing parameter of Ti-45Al-5Nb-0.3Y alloy is determined as 1 200 °C, 0.01 s −1 . The flow stresses are decreased by yttrium addition under the same compressive conditions. The activation energies of deformation Q are calculated as 448.6 and 399.5 kJ/mol for Y-free and Y-containing alloys, respectively. The deformed microstructure observation under 1 200 °C, 0.01 s −1 condition indicates that Ti-45Al-5Nb-0.3Y alloy shows more dynamic recrystallization. The improvement of hot deformability of Ti-45Al-5Nb-0.3Y alloy induced by yttrium addition should be attributed to that the smaller the original lamellar colonies, the lower the deformation resistance and activation energy of deformation are, and the more the dynamic recrystallization is.

Microstructure and dry wear properties of Ti-Nb alloys for dental prostheses

The microstructure and properties of a series of binary Ti-Nb alloys for dental prostheses with niobium contents ranging from 5% to 20% were investigated. The experimental results indicate that the crystal structure and morphology of Ti-Nb alloys are sensitive to their niobium contents. When Nb content is 5%, the acicular α crystal grain is observed. When Nb content is 10%, the coarse equiaxed crystal grain and the fine, acicular α crystal grain are observed. When Nb content is 15%, only the α equiaxed crystal grain is observed. When the alloy contains 20%Nb, the equiaxed and dendritic α crystal grain are observed. For Ti-Nb alloys, the increase of Nb content modifies the microstructure of Ti-Nb alloys significantly and decreases their compression elastic modulus, in which Ti-20Nb alloy shows the largest compression strength and Ti-5Nb alloy shows the best plasticity. The dry wear resistance of Ti-Nb alloys against Gr15 ball was investigated on CJS111A ball-disk wear instrument. For Ti-Nb alloys, Ti-10Nb alloy shows a smallest steady friction coefficient, Ti-5Nb alloy shows the smallest wear depth and best wear resistance, and Ti-15Nb alloy shows the largest wear depth and worst wear resistance. The phenomenon of furrow cut happens and furrows form during wear tests.

Microstructures and mechanical properties of hot-pack rolled Ti-43Al-9V-Y alloy sheet

Abstract Ti-43Al-9V-Y alloy sheets with dimensions of 300 mm×100 mm×(1.5–2) mm were produced by hot-pack rolling. After rolling, the microstructure of Ti-43Al-9V-Y alloy sheet becomes near gamma(NG), which is comprised of γ+ B 2 phases. After heat treatment(HT) at 1 200−1 320 °C for 30 min followed by furnace cooling(FC), network shape structure of B 2 phases in as-rolled microstructure is retained on the whole. Moreover, with increasing the HT temperature, precipitation of B 2 phase lamellae in equiaxed γ grains is increased. Equiaxed γ grains transform partly to α 2 /γ/ B 2 lamellar structure after the heat treatment at 1 320 °C for 30 min. Tensile test results show that room-temperature yield strength(YS) and ultimate tensile strength(UTS) of the as-rolled material are 509 and 612 MPa, respectively. With the test temperature increasing, the YS and UTS of the as-rolled are decreased, but the elongation is improved. After HT at 1 200 °C, both yield strength and fracture strength of Ti-43Al-9V-Y alloy sheet are the lowest. With HT temperature increasing, fracture strength is increased obviously, but yield strength of the sheet after HT at 1 280 °C is the highest, about 869 MPa.

Interfacial reactions between Ti-1100 alloy and ceramic mould during investment casting

Abstract The characteristics of the interfacial reaction between Ti-1100 melt and different primary coating materials was investigate. The effect of refractory materials and mould temperature on the reaction was analyzed by comparing the thickness, distribution of elements and microhardness of α-case layer. The α-case layer thickness of Ti-1100 casting with ZrO 2 primary coating is approximately 38 μm, which is higher than that with Y 2 O 3 primary coating (18 μm). Ti-1100 casting using ZrO 2 primary coating shows higher surface microhardness than that using Y 2 O 3 primary coating. The higher mold temperature results in more severe interfacial reaction. With the same primary coating material and mould temperature, Ti6Al4V alloy presents better stability than Ti-1100 alloy.

Microstructure and mechanical properties of TiAl-based alloy prepared by double mechanical milling and spark plasma sintering

Abstract A fine-grained TiAl alloy with a composition of Ti–45Al–2Cr–2Nb–1B–0.5Ta–0.225Y (mole fraction, %) was prepared by double mechanical milling(DMM) and spark plasma sintering(SPS). The relationship among sintering temperature, microstructure and mechanical properties was studied. The results show that the morphology of double mechanical milled powder is regular with size in the range of 20–40 μm and mainly composed of TiAl and Ti3Al phases. The main phase TiAl and few phases Ti3Al, Ti2Al and TiB2 were observed in the SPSed alloys. For samples sintered at 900 °C, the equiaxed crystal grain microstructure is achieved with size in the range of 100–200 nm. With increasing the SPS temperature from 900 °C to 1000 °C, the size of equiaxed crystal grain obviously increases, the microhardness decreases from HV658 to HV616, and the bending strength decreases from 781 MPa to 652 MPa. In the meantime, the compression fracture strength also decreases from 2769 MPa to 2669 MPa, and the strain to fracture in compression increases from 11.69% to 17.76%. On the base of analysis of fractographies, it shows that the compression fracture transform of the SPSed alloys is intergranular rupture.