Novel cobalt base superalloy and its high-temperature flow behavior

A novel cobalt base superalloy containing titanium and aluminum was investigated through metallography, tensile test, and high-temperature isothermal compression deformation. The results show that proper content of titanium and aluminum with can improve the strength and ductility of the cobalt base superalloy. The Co3（Ti,Al） compound with L12 structure precipitates when the novel superalloy is aged at 800℃ for 20 h. The e phase with hcp structure also precipitates when the superalloy is deformed by 28% and then aged at 650℃ for 4 h. The e phase can exist at 800℃. The superalloy has excellent high-temperature mechanical properties. Its maximum flow stress at 850℃ is in the range of 360-475 MPa when the strain rate is between 0.0021 and 2.1 s^-1. The flow stress of the superalloy during high-temperature deformation can be described by the Zener-Hollomon parameter with a hot deformation activation energy of 397 kJ.mol^-1.

Microstructure and Eutectic Transformation of Squeeze Casting Alumina/Zinc Alloy Composites

Alumina fiber-reinforced zinc alloy composites were manufactured by squeeze casting, and the eutectic transformation in the zinc alloy composites was studied. The results indicate that there is a fine and close interface between the fiber and the matrix, and the alloy elements can improve the combination between the fibers and the matrix in the composites. The fibers can serve as the sites of heterogeneous nucleation of the eutectic in the zinc alloy during the solidification of the composites, and the silicon on the interface between the fibers and the matrix plays a leading role during the coupled growth of the eutectic so that the eutectic transformation of the composites consists of Al-Si eutectic transformation and Zn-AI eutectic transformation.

Effects of Composition on Microstructure and Crystallization Behavior for Impact Polypropylene Copolymer Investigated by Restructuring the Complex Core-Shell Dispersed Particles in Ternary Blends

A series of ternary blends of polypropylene/ethylene-propylene random copolymer/ethylene-propylene segmented copolymer（HPP/EPR/Eb P） whose microstructures are similar to those of impact polypropylene copolymer（IPC） were prepared in order to systematically investigate the effects of composition on microstructure and crystallization behavior of IPC. The observation of primary phase morphology reveals that the dispersed phase with core-shell structure could be rebuilt in certain composition and excessive EPR leads to a bicontinuous phase structure in ternary blends. After undergoing same quiescent crystallization including isothermal and non-isothermal crystallization, these blend samples exhibit special composition-dependent melting behavior, i.e., the melting point increases markedly with the increase of EPR content until it turns down at a critical content（about 30 wt%）. The crystallization behavior is mainly ascribed to the different nucleation abilities. It is suggested that although the compatibility between EPR and HPP components becomes worse with the increase of EPR content due to the increased interfacial area and the decreased concentration of Eb P, higher EPR content in the blend facilitates to heterogeneous nucleation except for the appearance of obvious bicontinuous phase structure.

Preparation of FePd-RGO Bimetallic Composites with High Catalytic Activity for Formic Acid Electro-Oxidation

FePd-RGO composites through the growth of uniformly dispersed iron-palladium bimetallic nanoparticles （NPs） on reduced graphene oxide （RGO） nanosheets were prepared by a two-step method. The firstly formed Fe is used as the seed for the subsequent Pd growth. The formation of Fe NPs on RGO in the first step is performed by an in-situ reduction reaction with the reducer ethylene glycol under oil bath at 180 ℃. NPs in the as-prepared FePd-RGO have an average particle size of 6.5 nm, and Pd is added to one side of Fe which leads to the formation of Fe-Pd bimetallic interfaces. As compared with the commercial Pd black at the same loading, the composites have higher electro-catalytic activity, better electrochemical stability and higher resistance to CO poisoning for formic acid electro-oxidation.