Yi Min Gao

Phonon optics, thermal expansion tensor, thermodynamic and chemical bonding properties of Al4SiC4 and Al4Si2C5: a first-principles study

The phonon spectra, chemical bonding, thermal and thermodynamic properties of Al4SiC4 and Al4Si2C5 are calculated by first-principles using density functional theory. Raman and infrared (IR) active phonon modes and their eigenvectors are analyzed. Phonon mode-Grunseisen parameter and macroscopic Grunseisen constants are evaluated from phonon spectra. Employing quasiharmonic approximation (QHA), the thermal expansion tensor is obtained. The calculated volumetric thermal expansion coefficient (TEC) of Al4SiC4 is high than that of Al4Si2C5; and the linear TEC in the [001] direction is slightly higher than that of the [100] direction for both compounds. The computed average linear TECs for Al4SiC4 and Al4Si2C5 are 9.96 × 10−6 K−1 and 8.9 × 10−6 K−1 in a range from room temperature to 1500 K, respectively. Other thermal properties such as specific heats (CV, and CP), entropy (S), isothermal and isobaric bulk moduli (KT and KS) are also discussed. Using Slacks model, it is found that thermal conductivities are 59.9 W m−1 K−1 and 78.3 W m−1 K−1 at room temperature for Al4SiC4 and Al4Si2C5, respectively. The response of chemical bonds to hydrostatic pressure is discussed using Milliken population analysis. We also plot the charge density and its reduced density gradient to reveal the covalent bonds in the structure.

Effect of fluctuation, modification and surface chill on structure of 20%Cr hypereutectic white cast iron

Abstract The microstructural refinement of a cast hypereutectic Fe–20Cr–4C alloy using modification, surface chill and a novel fluctuation approach has been studied. Fluctuation involves the addition during pouring of powder or liquid metal to produce variations in temperature and/or composition in microareas of the liquid near the solidification front. The structures of the alloy were investigated using optical microscopy and image analysis. Increasing the degree of fluctuation (ferroalloy powder) resulted in finer primary and eutectic carbides. The combination of fluctuation with the addition of modifying agents (Fe–Si–Re alloy, aluminium and a laboratory intermediate alloy) and the application of surface chill, was found to increase the refinement of the carbides.

Effect of Ti addition on morphology and size of primary M7C3 type carbide in hypereutectic high chromium cast iron

Abstract Effect of Ti addition on the morphology and size of primary M7C3 type carbide in hypereutectic high chromium cast iron was investigated. The results indicated that the carbide is refined gradually, and its morphology becomes more equiaxed as titanium addition increases, but rather slowly when Ti addition exceeds 0·95%. The qualitative measurement result indicated that value shape factor K increases clearly first and then changes little, and the average equivalent diameter D changes against K exactly. Furthermore, by TEM analysis and Brammit’s theory calculation, the results also indicated that there are orientation relationships of TiC||M7C3 and [011]TiC||[0001]M7C3 between M7C3 type carbide and TiC, and the lattice misfit δ between TiC and M7C3 is 1·32%, explaining that TiC may provide the effective substrate plane for M7C3 nucleation to ameliorate morphology and size of primary M7C3 type carbide.

Interface Property and Two-Body Wear Behavior of High-Cr WCI Matrix Composite Reinforced with CC Particles

The vacuum infiltration casting process was adopted to prepare cemented carbide (CC) particles reinforced high-Cr white cast iron (WCI) composite by using failed CC parts as reinforcement. The interfacial structures between the CC particle and iron matrix were analysed by optical microscope (OM) and X-ray diffraction (XRD); the wear behavior of the composite was studied by pin-on-disc wear tester. The results showed that: owing to partial dissolution of the CC particles and diffusion of elements such as W, C, Cr and Fe, compounds such as Fe3W3C and Co3W3C were formed, which ensured metallurgical bonding at the interface; the wear resistance property of the composite was much higher than that of the heat treated WCI, moreover, when the applied load increased from 0.4Kg to 2Kg, the wear resistance value of the composite was more than 3.5 times than that of the heat treated WCI. However, there was no significant difference in the wear loss between CC/WCI composite and WC/WCI composite.

Effects of Forging and Heat Treatment on Microstructure and Properties of High Boron White Cast Iron

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.

Preparation of Warm Compacted and Sintered WC/Carbon Steel Composite and its Wear-Resistance

The WC particulates (0.076mm~0.100mm in size) and carbon steel (0.45wt% C) are selected as a reinforced phase and matrix in the composites. The techniques of warm compaction are systematically investigated with powder metallurgy solid phase sintering method. The performance of sliding friction wear of the composites is tested on a pin on disk tester. The test results of warm compaction show that the composites sample containing 50% WC and 50% steel possesses the perfect compaction density (9.4362g/cm3) and the relative density reaches 91.6% under the condition of 140°C compaction temperature, 320KN stress, and lubricated with zinc stearate. The results of wear test show that the composite sample under the condition of warm compaction gains the best wear property, and the relative wear resistance is the 2.9 times of 15Cr cast iron, 2.6 times of 20Cr cast iron and 2.8 times of the composite sample under the condition of room temperature compaction. And the wear mechanism of the particle-reinforced composites is analyzed using SEM.

Manufacture and Microstructures of Fe-Cr-C Hypereutectic In Situ Composites

In the present study, a Fe-Cr-C hypereutectic alloy was prepared from industry-grade materials and subjected to modification and fluctuation, through which new types of particle reinforced composites, hypereutectic in-situ composite, was generated. The structures of the composite modified or not with the range of fluctuation addition from 0% to 2.8wt.%, were investigated. The primary carbides were refined with the addition of modifying agents and fluctuations. Increasing the amount of fluctuation resulted in finer primary carbides. At 1380oC, with the addition of modifying agents and 2.8wt.% fluctuation addition, the structure was well modified.

Microstructure and Properties of Fe-B-C Cast Wear-Resistant Alloy

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.

Effect of Heat Treatment on Microstructures and Mechanical Properties of Al-Modified Boron High Speed Steel

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

Hot deformation and processing maps of Fe–B alloy

Abstract 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).