Phase composition, transition and structure stability of functionally graded cemented carbide with dual phase structure

The phase composition, phase transition and phase structure transformation of the wire-cut section of functionally graded WC-Co cemented carbide with dual phase structure were investigated by XRD phase analysis. It is shown that the composition of η phase in the core zone is Co_3W_3C (M_6 C type). The structure of cobalt based solid solution binder phase is fcc type. At the cooling stage of the sintering process, the phase transition of η phase, i.e. M_6C→M_12C and the martensitic phase transition of the cobalt based solid solution binder phase, i.e. fcc→hcp are suppressed, which facilitates the strengthening of the alloy. Because the instantaneous temperature of the discharge channel is as high as 10 000 ℃ during the wire cutting process, the processed surface is oxidized. Nevertheless, the oxide layer thickness is in micro grade. In the oxide film, η phase is decomposed into W_2C and CoO, and cobalt based solid solution binder is selectively oxidized, while WC remains stable due to the existence of carbon containing liquid organic cutting medium.

TEMPERING RESPONSE OF A DEFORMED LOW CARBON DUAL PHASE STRUCTURE

The low carbon dual phase structure was cold de formed first,then was tempered at 200 to 600℃.The variation in strength and ductility during tempering of the steel was investigated.It was found that a fter the de formed dual phase structure was tempered at 200 to 600℃, with the increase in the tempering temperature the tensile strength decreases rapidly;the lotal elongation remains constant at 200 to 500℃ but began to rise dramatically at a critical temperature between 500 and 600℃.However,when the non-deformed dual phase structure was tempered at the same temperature range,the tensile strength decreases and the total elongation increases continuously with the increase of temperature.It was demonstrated from TEM analysis that precipitating carbides density along the boundaries ofmartensite lath and the recrystallized grains are responsible for the tempering response ofthe de formed dual phase structure.

Phase precipitation and isothermal crystallization kinetics of FeZrB amorphous alloy

The crystallization process of Fe78ZrTBls （at%） amorphous ribbon was investigated by Xray diffraction （XRD）, differential scanning calorimetry and scanning electron microscopy （SEM）. The fully amorphous structure of asquenched （Aq） ribbons was confirmed by XRD pattern. The saturation magnetization （Ms） and Curie tem perature of the Aq ribbon were measured as 124.3 （A.mZ）＆g and 305 ℃ with vibrating sample magnetometer （VSM）, respectively. When the ribbons was annealed at 550 ℃ near the first onset temperature （Txl = 564.9 ℃）, the Ms was increased by 17 %, which was caused by the formation of a dual phase structure. The isothermal crystallization kinetics and crystallization mechanism of primary ctFe phase in the dual phase structure were studied by Arrhenius and JohnsonMehlAvramiKolmogorov equations respectively. The results showed that the crystallization of Fe phase was a diffusioncontrolled surface nucleation growth process, and the nucleation rate decreased with longer crystallization time.

High-entropy alloy and amorphous alloy composites fabricated by ultrasonic vibrations

We successfully fabricate high-entropy alloys and amorphous alloy composites by adopting the proposed ultrasonic vibration method.The low-stress,low-temperature method enables us to create composites that combine both amorphous and crystalline properties.Microscopic observations and computed tomography measurements indicate good bonding quality without pores or cracks in the composites.Due to the unique structure which mixes soft and rigid phases,the composite exhibits improved mechanical performance compared to that obtained from a pure single phase.Our results are promising for the manual design and fabrication of smart materials containing multiple phases and compositions.