Effect of lower bainite/martensite/retained austenite triplex microstructure on the mechanical properties of a low-carbon steel with quenching and partitioning process

We present a study concerning Fe-0. 176C-1.31Si-1.58Mn-0.26Al-0.3Cr （wt%） steel subjected to a quenching and partitioning （Q＆P） process. The results of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and tensile tests demon- strate that the microstructures primarily consist of lath martensite, retained austenite, lower bainite （LB）, and a small amount of tempered martensite; moreover, few twin austenite grains were observed. In the microstrucmre, three types of retained austenite with different sizes and morphologies were observed： blocky retained austenite （-300 nm in width）, film-like retained austenite （80-120 nm in width）, and ul- tra-fine film-like retained austenite （30-40 nm in width）. Because of the effect of the retained austenite/martensite/LB triplex microstructure, the specimens prepared using different quenching temperatures exhibit high ultimate tensile strength and yield strength. Furthermore, the strength effect of LB can partially counteract the decreasing strength effect of martensite. The formation of LB substantially reduces the amount of retained austenite. Analyses of the retained austenite and the amount of blocky retained austenite indicated that the carbon content is critical to the total elongation of Q＆P steel.

Microstructural evolution and mechanical properties of a low-carbon quenching and partitioning steel after partial and full austenitization

In this work, low-carbon steel specimens were subjected to the quenching and partitioning process after being partially or fully austenitized to investigate their microstructural evolution and mechanical properties. According to the results of scanning electron microscopy and transmission electron microscopy observations, X-ray diffraction analysis, and tensile tests, upper bainite or tempered martensite appears successively in the microstructure with increasing austenitization temperature or increasing partitioning time. In the partially austenitized specimens, the retained austenite grains are carbon-enriched twice during the heat treatment, which can significantly stabilize the phases at room temperature. Furthermore, after partial austenitization, the specimen exhibits excellent elongation, with a maximum elongation of 37.1%. By contrast, after full austenitization, the specimens exhibit good ultimate tensile strength and high yield strength. In the case of a specimen with a yield strength of 969 MPa, the maximum value of the ultimate tensile strength reaches 1222 MPa. During the partitioning process, carbon partitioning and carbon homogenization within austenite affect interface migration. In addition, the volume fraction and grain size of retained austenite observed in the final microstructure will also be affected.

In situ backscattered electron imaging study of the effect of annealing on the deformation behaviors of Ni electroformed from additive-free and saccharin-containing sulfamate solutions

The Ni samples were electroformed from additive-free(AF) and saccharin-containing(SC) sulfamate solutions, respectively. In situ backscattered electron(BSE) imaging, electron backscatter diffraction(EBSD), and electron-probe microanalysis(EPMA) were used to investigate the effect of annealing on the deformation behaviors of the AF and SC samples. The results indicate that columnar grains of the as-deposited AF sample had an approximated average width of 3 μm and an approximated aspect ratio of 8. The average width of columnar grains of the as-deposited SC sample was reduced to approximately 400 nm by the addition of saccharin to the electrolyte. A few very-large grains distributed in the matrix of the SC sample after annealing. No direct evidence indicated that S segregated at the grain boundaries before or after annealing. The average value of the total elongations of the SC samples decreased from 16% to 6% after annealing, whereas that of the AF samples increased from 18% to 50%. The dislocation recovery in grain-boundary areas of the annealed AF sample was reduced, which contributed to the appearance of microvoids at the triple junctions. The incompatibility deformation between very-large grains and fine grains contributed to the brittle fracture behavior of the annealed SC Ni.

Microstructure and phase composition of hypoeutectic Te–Bi alloy as evaporation source for photoelectric cathode

A hypoeutectic 60Te–40Bi alloy in mass percent was designed as a tellurium atom evaporation source instead of pure tellurium for an ultraviolet detection photocathode.The alloy was prepared by slow solidification at about 10^(-2) K·s^(-1).The microstructure,crystal structure,chemical composition,and crystallographic orientation of each phase in the as-prepared alloy were investigated by optical microscopy,scanning electron microscopy,X-ray diffraction,electron backscatter diffraction,and transmission electron microscopy.The experimental results suggest that the as-prepared 60Te–40Bi alloy consists of primary Bi_2Te_3 and eutectic Bi_2Te_3/Te phases.The primary Bi_2Te_3 phase has the characteristics of faceted growth.The eutectic Bi_2Te_3 phase is encased by the eutectic Te phase in the eutectic structure.The purity of the eutectic Te phase reaches 100wt%owing to the slow solidification.In the eutectic phases,the crystallographic orientation relationship between Bi_2Te_3 and Te is confirmed as[0001]_(Bi2 Te3)//[1213]_Te and the direction of Te phase parallel to[1120]_(Bi2 Te3)is deviated by 18°from N(2111)_Te.

Effects of Mo Contents in Matrix on Microstructure and Properties of Vanadium Carbide Coating Formed by Thermal Diffusion Treatment

Thermal diffusion salt-bath vanadizing was finished for Crl2MoV die steel, in order to investigate the properties of vanadium carbide coatings related with the Mo contents in Crl2MoV die steel. Scanning electron micro- scopic observation reveals that Mo can decrease the growth rate of coating as a carbide forming element. Besides, Mo element can promote grain refinement of the coating. X-ray diffraction analysis shows that the different Mo contents have no influence on the phase structure of the coatings. Energy dispersive spectrum analysis and mechanical properties test show that Mo can diffuse into the coating and make a strengthening effect on the coating.

Electrochemical properties of niobium and phosphate doped spherical Li-rich spinel LiMn2O4 synthesized by ion implantation method

Spherical Li-rich lithium manganese oxide（LMO） spinel material was synthesized by an ion implanted method assisted by polyalcohol doped with Niobium and Phosphate simultaneously.The material was characterized by scanning electron microscopy,X-ray diffraction and BET specific surface area analysis.The electrochemical performances were investigated with galvanostatic techniques and cyclic voltammetry.The synthesis process was investigated with TG/DSC.The results show that the lithium ion can be immersed into the pore of manganese dioxide at a low temperature with the ion implanted method.The prepared materials have a higher discharge capacity and better crystallization than those prepared by solid phase method.The doped Nb can improve the capacity of the Li-rich LMO spinel and reinforce the crystal growth along（111） and（400） planes.The crystal grains show circular and smooth morphology,which makes the specific surface area greatly decreased.Phosphate-doped LMO spinel exhibits good high-rate capacity and structure stability.The prepared Li（1.09）Mn（1.87）Nb（0.031）O（3.99）（PO4）（0.021）delivers a discharge capacity of 119mAhg^-1 at 0.2C（1C=148mAg^-1） and 112.8 mAhg^-1 at 10 C,the discharge capacity retention reaches 98% at 1 ℃ after 50 cycles at 25 ℃ and 94% at 55 ℃.