Study on microstructure and property of K418B superalloy wide gap brazed joints

Wide gap brazing（WGB） experiments using the butted specimen with a 1.5 mm gap were carried out for the repair of the failed K418B superalloy low-pressure turbine vanes.The high temperature creep rupture strengths of the brazed joints were tested,and the microstructures and fracture surfaces of the joints were observed.The results show that the microstructure of K418B alloy joint is composed of dense equiaxed grain,small and discrete compounds with a few micro-pores.During the creep rupture test,the cracks initiate preferentially at the micro-pore or the grain boundary,then propagate along the grain boundary till the fracture happens.The creep rupture strength at 700 ℃ of the brazed joints with 50% braze metal in the working part could exceed 90% that of the K418B superalloy,and the joints with 100% braze metal in the working part achieve 70% to 80% of the creep rupture strengths for the K418 B base metal.

Distinct microstructure and property evolution of 0.76(Bi_(0.5)Na_(0.5))TiO_(3)-0.24SrTiO_(3) ferroelectric ceramics synthesized with different TiO_(2) reactants

Single phase 0.76(Bi_(0.5)Na_(0.5))TiO_(3)–0.24SrTiO_(3) ferroelectric ceramics have been synthesized with homogenous anatase and hierarchical rutile TiO_(2) raw reactants(BNST-A and BNST-R).Either calcined powder persists the microstructure characteristics of raw reactants.As the result,when the sintering temperature increases from 1000 to 1200℃,the average grain size and density of BNST-A increase from 0.49 to 1.48μm and 5.02 to 5.61 g/cm^(3),while those of BNST-R from 0.86 to 1.44μm and 5.37 to 5.61 g/cm^(3).BNST-A illustrates a predominant ergodic relaxor state,and BNST-R prefers a non-ergodic relaxor state,as evidenced by the distinct polarization-electric field loops and current-electric field curves.Especially,such a distinct ferroelectric state is independent of sintering temperature.It is believed that the special hierarchical microstructure of rutile TiO_(2) reactant is beneficial to form denser ceramics with larger grains,and thus suppresses the contributions of polar nanoregions and defect-induced built-in field to ferroelectric property,leading to non-ergodic relaxor state.This work clearly demonstrates the nonnegligible effects of TiO_(2) reactants on the microstructure and properties of BNST ferroelectric ceramics.

Effect of RE-Modifier on Microstructure and Mechanical Property of High-Carbon Medium-Manganese Steel

The effect of RE-modifier on the microstructure and mechanical properties of high carbon-medium manganese steel has been investigated in present work.The results showed that the RE-modifier can refine the crystalline grain of high-carbon medium-manganese steel.The shape and distribution of carbides are improved and the columnar grains and phosphide in grain boundary are eliminated.Consequently,the impact toughness of the steel is increased by more than one time,compared with no addition of RE-modifier.

Effect of Rare Earth (Niobium) on Costed and Hot-Rolled Microstructure and Properties of Heavy Rail Steels

A compared investigation was made on the microstructure and mechanical properties of continuous casting square blanks of BNbRE and U71Mn heavy rail steels having eutectoid composition. The variation of solidified structure of the square blanks was demonstrated by measuring hardness. The observation to the structure and inclusions in the head, waist and base of the hot-rolled rails of the test steels were carried out with optical microscope and SEM. It is found that the casting blanks of both tested steels compose of three areas with constant hardness and three hardness varying areas, and there is considerable P-eutectic structure in the blank of the U71Mn steel. The distribution of the inclusions in the UT1Mn steel rail is mainly oxides in both rail head and rail base, and is mainly MnS in the waist of the rail. There has strong effect of the addition of rare earth elements on them. The discussion on these results was made.

Internal Friction and Profile of Property and Structure of PD_3 and PD_3RE Rail Steels

The profile of both hardness and microstructure of continuous casting blanks and rails of PD3 heavy rail steel and PD3RE steel containing small amount of rare earth （RE） added from tundish were studied. It is found that the addition of RE makes the fluctuation of the hardness value decrease, and inhibits effectively and/or even removes lower hardness value（zone） in the centric area of the blank with a cross section of 280 mm × 380 mm, and that the surface layer in the rail head of PD3RE steel is obviously hardened and the reason causing this hardening is due to the thinning of the pearlite structure. The metallographic observation shows that there exists a Fe-P（C） eutectic structure in the blank center of the PD3 steel containing only 0. 016% P, while the addition of RE can fully inhibit this structure.

Characteristics of Nd： YAG laser welded 600 MPa grade TRIP steel

Microstructures and mechanical properties of Nd ： YAG laser welded transformation induced plasticity （TRIP） steel with tensile strength of 645 MPa were studied. Due to high cooling speed of laser welding, the weld metal mainly consists of martensite different from the base metal, which is composed of ferrite matrix with bainite and a little retained austenite. Therefore, the weld metal has maximum hardness at welded joint. The yield strength and tensile strength of welded specimens tested perpendicular to weld line were almost equal to those of the base metal. But the yield strength and tensile strength of welded specimens tested parallel with weld line were a little higher than those of the base metal. The formability of laser welded TRIP steel was decreased compared with that of the base metal.

Nondendritic Microstructure of 6061 Alloy Obtained by Electromagnetic Casting and Thixoformed Properties

Abstraet:The semi-solid 6061 aluminum alloy castings with t'me equiaxed nondendritic grains are obtained by means of electromagnetic casting method.Appropriate casting technical parameters are casting temperature---720 ℃,casting speed---100 mm/min,cooling water amount---0.09 m^3/min.The temperature field in the electric stove reheated to the liquid-solid zone is homogeneus and the prope reheating temperature is 630 ℃.When the mould temperature is 300-500 ℃,the parts used in automobiles can be thixoformed successfully,its σ_b is 392 MPa,vigid 142.3 HV and δ_5 11.5%after T6 heat treatment.

Effect of RE element Y on properties of Ti(C, N)-based cermet

The effect of RE element Y on the microstructure and properties of Ti(C,N)-based cermet has been investigated. Yttrium can refine the particles of carbide phase because itcan purify the interface between binder phase and carbide phase, and increase the thickness of rimphase slightly. The effect is in the most evidence when the mass fraction of Y is 0.8 percent andwhen the transverse rapture strength and the hardness of Ti(C, N)-based cermet are maximal.

Development and Application of Non-Quenched and Tempered Steel for Auto Forging Components in China

Non-quenched and tempered (NQT) steels have been applied for auto forging products at the aim of lower cost since 1980’s in China.Without quenching and tempering processes,the cost of heat treatment was greatly decreased,so they are widely applied in car forgings such as crankshaft,connecting rod.Recently,with the aim of improving performance and reducing production cost,new technologies,such as:reductions of microalloyed elements,microstructure refining,and mechanical properties forecast have been developed in China auto industry.The designation,processing,properties prediction and microstructure of auto components have been controlled comprehensively.With the development of new technologies,NQT steel gradually began to be applied to product important parts,and replace Quenching and Tempering (QT) steels.Both steel makers and end product users are expressed their desire to share benefits of technological innovation.The technologies will have a huge developing space and very bright developing prospects in motor parts industry in future.

Preparation of N-Doped Bi_2WO_6 Microspheres for Efficient Visible Light-Induced Photocatalysis

The N-doped bismuth tungstate （BizWOt） photocatalysts with high visible light activity were prepared by the hydrothermal method using urea as a nitrogen source. The as-prepared N-doped Bi2WO6 samoles were characterized by X-ray diffraction, scanning electron microscopy, specific surface area, photocurrent analysis, and UV-Vis diffuse re- flectrance spectroscopy. The photocatalytic activity was evaluated by photocatalytic degradation of rhodamine B （RhB） solution under visible light irradiation. The photocatalytic mechanisms were analyzed by active species trapping experi- ments which revealed that the holes were the main active species of N-doped BizWO6 products in aqueous solution under visible light irradiation, rather than .OH and O-. With the assistance of H202, the photocatalytic activity for degradation of RhB could be further improved because H202 reacted with conduction band electrons to generate more hydroxyl radicals. KEY WORDS：