Search

The mechanical, electronic and thermal physical properties of A-type R 2 O 3 (R=Y, La) under hydrostatic pressure are studied by first-principles calculations. The calculated band gap is 6.3 eV (5.9 eV) for Y 2 O 3 (La 2 O 3 ). Under hydrostatic pressure, both phases show anisotropic elasticity in different crystallographic directions. The isothermal bulk modulus of R 2 O 3 decreases monotonically with the increasing of temperature from 300 K to 1500 K. The intrinsic ductile nature of both phases is confirmed by the obtained B / G ratio. The temperature dependence of linear TECs of La 2 O 3 is stronger than that of Y 2 O 3 , and the linear TECs in [001] direction show larger values in both phases than those in [010] direction. At room temperature, the average linear TECs for Y 2 O 3 and La 2 O 3 are 8.40×10 −6 K −1 and 8.42×10 −6 K −1 , respectively. Other thermal physical properties such as specific heats ( C V , and C P ), entropy ( S ), sound velocity and Debye temperature are also obtained.

The microstructure, toughness, hardness and wear resistance of Fe-B-C cast wear-resistant alloy were studied. The results indicate that, the as-cast Fe-B-C alloy comprises pearlite, ferrite and eutectic phase Fe2 (B, C), and that, with increasing boron and carbon contents, the boride volume fraction (BVF) and macrohardness increase; furthermore, when boron content increases from about 0.5 wt.% to 2.0 wt.%, the increase trend of the macrohardness will become smaller with increasing the carbon content. The results also indicate that, after heat-treatment, the Fe2 (B, C) becomes coarser than that as cast condition, and the boron content has less effect on the martensite hardness at the same carbon content; with increasing boron and carbon contents, the hardness of the samples increases and inversely the toughness decreases. At a lower BVF, the matrix plays a dominant role on the impact toughness of Fe-B-C alloy; however, at a higher BVF, the BVF plays a dominant role. The wear test results indicate that, with increasing the boron and carbon contents, the weight loss of the samples decreases, namely, the increase of wear resistance.

Boron-bearing high speed steels are widely used in roller materials because of their improved wear resistance and toughness. In present work, aluminum was added into boron high speed steel and the aging-hardening behavior and microstructures of tempered boron high speed steel at various tempering temperatures were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Energy dispersive spectrometry (EDS) and HR-150A Rockwell hardness tester. The results show that the bulk hardness of boron high speed steel gradually enhances with the increasing destabilized temperature. Aluminum addition cuts down the bulk hardness and delays the hardening process, thus leading to high the hardening value of boron high speed steel shifting to higher destabilized temperature. After tempering process, boron-bearing high speed steel displays precipitate-hardening behavior at the tempered temperature of about 520°C. The bulk hardness of boron-bearing high speed steel achieves 60.5 HRC as a maximum value when the aluminum addition is 0.6 wt.%. More aluminum addition can result in lower precipitate-hardening rate and bulk hardness. The microstructures of boron high speed steel tempered at 520°C consist of eutectic borides and tempered martensite dispersed a lot of secondary precipitates. XRD and TEM results indicate that the precipitate-hardening properties of boron high speed steel depend on precipitates and square degree of martensite

An experimental investigation was presented in this paper on reinforced concrete box beams subjected to shear, torsion, and bending moment strengthened by carbon fiber reinforced polymer (CFRP). Eight box beams were cast and separated into two groups according to two different torque-to-shear and torque-to-bending moment ratios. Three box beams from each group strengthened by CFRP in different configurations and one control box beam were tested. The main parameters of this experiment were the different ratios and configurations, including U-jacket layers and U-jacket strips with or without longitudinal strips. The cracking and failure mode, effect of wrapping configuration, torsional capacity, and behavior of the different torque-to-shear and torque-to-bending moment ratios were studied in the paper.

The hot deformation behaviour of Fe–B alloy under hot compression conditions has been investigated in the temperature range of 1000–1075°C and strain rate range of 0·01–4 s−1. The results show that the maximum stress decreases with decreasing strain rate and increasing temperature, and the activation energy is 573·68 kJ mol−1. Processing maps are developed on the basis of experimental data and using the principles of dynamic materials model. The peak power dissipation efficiency domain occurs roughly in the temperature range of 1045–1075°C and strain rate range of 0·02–0·3 s−1 with a peak efficiency of power dissipation of ∼0·5, which is the optimal processing region for the investigated alloy. Microstructural observations reveal that the dynamic recrystallisation occurs in the domain. The alloy also exhibits flow instability in the temperature range of 1000–1075°C and higher strain rate (>0·5 s−1).

The present study investigates the effects of rare earth and aluminium on the microstructures of as cast and heat treated semisolid Fe–B cast alloys. The as cast microstructure of the semisolid modified Fe–B cast alloy consists of the eutectic boride, pearlite and ferrite. Moreover, compared to a net-like distribution of the coarse eutectic borides in the ordinary unmodified alloy, the eutectic boride structures in the semisolid modified alloy are greatly refined and less interconnected. After heat treatment, the phases in the semisolid modified Fe–B cast alloy consist of the boride and martensite. The additions of rare earth and aluminium help to promote the formation of the short rod shaped and round borides in the semisolid Fe–B cast alloy during heat treatment. Compared to the ordinary unmodified alloy, there is no significant change in the boride area fraction but an obvious decrease in average boride area in the semisolid modified alloy.

Microstructure and properties of isothermally quenched high boron white cast iron were investigated in this paper. The results show that the microstructure of high boron white cast iron is mainly composed of many continuous and netlike eutectic borides, pearlite and ferrite under as-cast condition. The microhardness of Fe2B ranges in 1200-1600HV whose value seems to approximate that of (Fe,Cr)7C3–type carbide (HV1200~1800) in high chromium white cast iron. After isothermal quenching, the matrix transforms into lower bainite in which carbide precipitations are arranged in parallel rows at an angle of 60 deg to the long axis of the plates, but the morphology of boride remains nearly unchanged compared with its as-cast condition. Moreover, precipitation particles with the size of about 1~4 μm can be found in the matrix of isothermally quenched high boron white cast iron. Impact fracture morphology of isothermally quenched high boron white cast iron indicates that fracture propagated more easily through boride/matrix interface than through matrix.

The influence of boron concentration on corrosion resistance of high boron white cast iron dipped into a pure liquid zinc bath at 460°C was investigated. The results reveal that high boron white cast iron containing 3.5 wt.%B exhibits excellent corrosion resistance due to the dense continuous netlike or parallel Fe2B phase which hinders the Fe/Zn interface reaction. The corrosion rate decreases significantly when the boron concentration increases, but the corrosion rate declines slightly when the boron concentration exceeds 3.5wt.%. EDS results indicate the coarse and compact δ phase generated near the matrix and a large amount of massive and blocky  phase occurred close to the liquid zinc. The corrosion process includes Fe/Zn interface reaction and the spalling and fracture of Fe2B. The failure of Fe2B is mainly caused by the microcrack of phase transformation.

This study investigates the effect of rare earth and aluminium composite modification on the structural variations of as-cast and heat treated medium carbon Fe–B cast alloys. The as-cast microstructure of Fe–B cast alloy consists of the eutectic boride, pearlite, martensite and ferrite. Moreover, compared to a netlike distribution of the coarse eutectic borides in the unmodified alloy, the eutectic boride structures in the modified alloy are greatly refined and less interconnected. After heat treatment, the phases in Fe–B cast alloy consist of the boride and martensite. The addition of rare earth helps to increase the number of the rod-shaped and round borides in Fe-B cast alloy during austenitizing. Compared to the unmodified alloy, the boride volume fraction and Rockwell hardness of the modified alloy have no significant change, however, the average area of each boride in the modified alloy is lower and the impact toughness is higher.

The effects of forging and heat treatment on microstructure and properties of high boron white cast iron were investigated in this paper. The results show that forging breaks up boride network and makes broken boride particles uniformly distributed in matrix. During subsequent heat treatment, spheroidized boride is able to be obtained. The hardness of high boron white cast iron increases slightly (from 51.4 HRC to 54.7 HRC) while the toughness increases obviously (from 5 J/cm2 to 107 J/cm2) by combined process of forging and heat treatment. Fracture morphology changes from brittle fracture to ductile fracture.

The aim of the present study is to investigate the effects of rare earth and aluminium on the structural variations of medium carbon Fe–B cast alloy under the same austenitising temperature and different austenitising times. It is observed that the as cast microstructure of Fe–B cast alloy consists of the eutectic boride, pearlite, martensite and ferrite. Moreover, the as cast eutectic boride structures are greatly refined, and a blocky, less interconnected boride network is obtained when rare earth and Al are added. After different austenitising times, in each case, the phases in modified Fe–B cast alloy consist of the boride and martensite. The addition of RE in Fe–B cast alloy accelerates the diffusion process of B and Fe atoms during austenitising. Based on this favourable condition, the numbers of the fractured boride networks and isolated granular borides increase with increase in austenitising time. The boride volume fraction, Vickers hardness of martensite matrix and boride, and Rockwell h...