Chen Yuyong

Effect of Y Addition on Microstructure and Mechanical Properties of TiAl-based Alloys Prepared by SPS

Abstract TiAl alloys with a composition of Ti-45Al-2Cr-2Nb-1B-0.5Ta(at%) (TA alloy) and Ti-45Al-2Cr-2Nb-1B-0.5Ta- 0.225Y(at%) (TAY alloy) were prepared by double mechanical milling and spark plasma sintering (SPS). The effect of Y addition on microstructure and mechanical properties of TiAl-based alloys was studied. The results show that the morphology of double mechanical milling powder is regular with sizes in the range of 20∼40 μm. The main phases of TiAl and Ti3Al and few phases of Ti2Al and TiB2 were observed in the SPS bulk samples of TiAl-based alloys. The equiaxed crystal grain microstructure was achieved with sizes in the range of 100∼400 nm in TA alloy samples. The samples exhibited compressive properties at room temperature with a compressive strength of 2614 MPa and a compression ratio of 20.57%. For TAY alloy, the sizes of equiaxed crystal grain obviously decreased. The samples exhibited compressive properties at room temperature with a compressive strength of 2677 MPa and a compression ratio of 22.91%. The micro-hardness of the SPS bulk samples of TA alloy was obviously higher than that of the SPS bulk samples of TAY alloy. On the base of analysis of fractographs, it showed that the compression fracture transform of the SPS TiAl-based alloys samples was intergranular rupture.

Electrochemical corrosion and bioactivity of Ti-Nb-Sn-hydroxyapatite composites fabricated by pulse current activated sintering

Ti-Nb-Sn-hydroxyapatite (HA) composites were prepared by mechanical alloying for different times (unmilled, 4, 8 and 12h), followed by pulse current activated sintering. The effects of the milling time on the electrochemical corrosion resistance and bioactivity of the sintered Ti-35Nb-2.5Sn-15HA composites were investigated. Potentiodynamic polarization test results indicated that the sintered Ti-35Nb-2.5Sn-15HA composites exhibited higher corrosion resistance with increasing milling time. The corrosion potential and current of the Ti-35Nb-2.5Sn-15HA composite sintered by 12h milled powders were - 0.261V and 0.18μA/cm2, respectively, and this sintered composite showed a stable and wide passivation region. The hemolysis rate of the sintered Ti-35Nb-2.5Sn-15HA composites reduced with increasing milling time and the lowest hemolytic rate of the composites was 0.87%. In addition, the in vitro cell culture results indicated that the composite sintered by 12h milled powders had good biocompatibility. These results indicate the significant potential of Ti-35Nb-2.5Sn/xHA composites for biomedical implant applications.

REVIEW OF THE INVESTMENT CASTING OF TiAl-BASED INTERMETALLIC ALLOYS

TiAl–based intermetallic alloys are emerging as a new generation light–weight, high temperature structural materials and possess wide capacities of engineering applications in aeronautics, space and automobile industries. Near–net–shape casting is a commonly used manufacturing method for TiAl–based alloys. In this paper, the evolution of the alloy design and investment casting technology of TiAl–based alloys are reviewed. The prospects of the investment casting of TiAl–based alloys are also represented.

HIGH TEMPERATURE CREEP AND FATIGUE BEHAVIOR AND LIFE PREDICTION METHOD OF A TiAl ALLOY

Creep (at 700 degrees C) and low cycle fatigue (at 700 and 750 degrees C) tests of Ti-43Al-9V-Y alloy with duplex (DP) and fully lamellar (FL) microstructures are carried out to study the creep, fatigue deformation and life prediction. Firstly, Omega method is employed to characterize the creep deformation and to predict the rupture life. Secondly, the proposed fatigue life model based on walker strain is employed to predict the fatigue life for these two types of TiAl alloy. The results show that: (1) high temperature creep curves of the material of both DP and FL microstructure contain steady and accelerated creep stages other than initial creep stage, and Omega method is able to characterize the creep deformation of TiAl alloy with DP and FL microstructure; (2) the rupture time of the material of FL microstructure is longer than that of DP microstructure, and the predicted rupture time by Omega method agrees well with the test data; (3) the fatigue life of DP is longer than that of FL under the same test condition, and the predicted fatigue life is well located in the scatter band of 3 of the test fatigue life.

Effect of Heat Treatment on Microstructure and Properties of as-Forged TiAl Alloy with β Phase

Abstract The canned forging pancake of Ti-45Al-5.4V-3.6Nb-0.3Y alloy was prepared, and the microstructure control and properties for various microstructures of as-forged alloy were studied. Three different microstructures, duplex, nearly lamellar and fully lamellar, were obtained through heat treatments. The microstructure evolution was analyzed and tensile properties were measured. The results show that the treated sample with duplex microstructure exhibits the best ductility, and its elongation reaches 1.35% the alloy with nearly lamellar microstructure has better strength, i.e.yield strength and fracture strength are 605.31 MPa and 665.75 MPa at room temperature, respectively.

Relationship Between Solidification Thermal Parameters, Dendrite Arm Spacing and Ultimate Tensile Strength in Al-4.5% Cu

ABSTRACT Relationship between solidification thermal parameters, dendrite arm spacing(DAS) and ultimate tensile strength(UTS) in Al-4.5%Cu alloy containing 0.1 to 0.5% misch metals was analysed by statistical analysis. It was shown that freezing index (f.i) and gradient acceleration parameter (GAP) were two efficient parameters to control dendrite arm spacing of this alloy. A nearly linear relationship was found between DAS and UTS of the alloy as follows: UTS = 33.61 - 0.16 DAS cc = 0.814. It is feasible to forecast UTS by measuring of DAS of the castings.