Development of boron white cast iron

Abstract

With boron substituting for carbon in cast iron composition and eutectic borides substituting for eutectic carbides in microstructure as the hard wear resistant phase, a new kind of wear resistant white cast iron has been developed. The microstructure and mechanical properties of this new white cast iron both in the as cast state and after appropriate heat treatments were studied. The results show that the as cast microstructure of the boron white cast iron comprises a dendritic matrix and interdendritic eutectics, and the eutectic compound is that of M₂B or M′_0˙9Cr_1˙1B_0˙9 type, where M represents Fe, Cr or Mn and M′ represents Fe or Mn. The morphology of the eutectic borides is much like that of carbide in high chromium white cast iron, but the hardness of boride is higher than that of carbide. The matrix in as cast microstructure comprises martensite and pearlite. After austenitising and quenching, the matrix mostly changes to lath type martensite and the eutectic borides remain unchanged. In addition, two different sizes of particles, with different forming processes during heat treatment, appear in the matrix. The boron white cast iron possesses higher hardness and toughness than conventional white cast iron and nickel hard white cast iron, and has a better balance between hardness and toughness than high chromium white cast iron.     

Effect of zinc plating of low carbon steel on corrosion resistance in cassava fluid environment

Abstract

This research work investigated the corrosion resistance of zinc plated low carbon steel in cassava fluid (i.e. containing hydrogen cyanide). It simulated the effect of continuous use of the material in a cyanide environment where corrosion products are left in place. Low carbon steel samples were zinc electroplated at voltages between 0˙5 and 0˙9 V for 5 to 20 min. The plated samples were then subjected to a cassava fluid environment for 30 days. The electrode potentials, in mV (SCE), were measured every day. Weight loss was determined at intervals of 5 days for duration of the exposure period. The result showed corrosion attack on the zinc plated steel, the severity increasing with increasing weight of zinc coating on substrate. The result showed that thinly plated low carbon steel did not have any advantage over unplated steel and were quickly stripped of their zinc plating with resultant corrosion of the underlying steel substrate. Heavily zinc plating steel was observed to offer some protection for the steel but not for a long time. The pH of the cassava solution which initially was acidic because of the cyanide content in the cassava was observed to progress to neutrality after 5 days and then became slightly alkaline at the end of the 30 days test (because of corrosion product contamination of the cyanide), contributing to the reduced corrosion rate. Unplated steel was found to be unsuitable for the fabrication of cassava processing machinery without some form of surface treatment, but unfortunately, zinc is not suitable as a protective coating in this environment.     

Oxidation behaviour of Ni–Cr based alloy containing Si during high temperature application in an oil burner

Abstract

In certain modern oil burners, the combustion reaction is started in a flame tube. In the combustion atmosphere, the tube material is exposed to high temperatures and temperature changes. Nickel–chromium alloys are used to meet the requirement of high oxidation resistance. The paper presents the results on the oxidation behaviour of the silicon containing alloy 603 exposed to a low NO_x burner at temperatures of 950 and 1000°C up to 2000 h. Beneath a chromia scale silica precipitates formed at the beginning of exposure, which grew laterally establishing a nearly continuous interlayer. The interlayer disintegrated during the continued exposure. A thinner chromia scale was observed for alloy 603 compared with the scales observed for aluminium containing nickel–chromium alloys. This was attributed to a pronounced scale spallation. After 1000 h at 1000°C catastrophic oxidation of alloy 603 occurred involving Mo oxide and internal chromium oxide.     

Influence of SiCp content and matrix composition on corrosion resistance in cast aluminium matrix composites in salt fog

Abstract

A study has been carried out into the influence of the proportion of SiCp and the matrix composition of four aluminium metal matrix composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p and A380/SiC/20p) on their salt fog corrosion behaviour. The matrix of the A360/SiC/xxp composites is virtually free of Ni and Cu while the A380/SiC/xxp matrix contains 1.39 - 1.44 wt-%Ni and 3.13 - 3.45 wt-%Cu. The kinetics of the corrosion process were studied using gravimetric tests. The nature of corrosion products was analysed by SEM and low angle XRD before and after accelerated testing to determine the influence of microstructural changes on corrosion behaviour during exposure to the corrosive environment. The extent of the corrosion damage to the Al/SiC composites depended on the concentration of nucleation sites and the matrix composition. One of these nucleation sites is in the interface region between the matrix and the particles. The corrosion process was influenced more by the concentration of alloy elements in the matrix than by the proportion of SiCp reinforcement.     

Duplex surface layer treatment of Al alloy: electron beam alloying and plasma nitriding

Abstract

Al alloys offer a high potential as lightweight construction materials due to their low density, specific strength and processing properties. However, the field of application is limited by their low hardness and poor wear properties. Duplex surface treatment combining electron beam (EB) alloying and plasma nitriding offers one possibility to produce hard and wear resistant surface layers on Al alloys. The EB alloyed surface layer acts as supporting layer for the hard AlN coating so that the load bearing capacity can be enhanced. In the present study duplex treatment of Al-5083 (AlMg4·5Mn0·7) Al alloy has been investigated. Before the EB treatment alloying material deposition was carried out by atmospherically plasma spraying. Various sandwich layers based on Al and Fe respectively, have been applied. Different beam deflection techniques have been tested and their effect on surface deformation, microstructure and hardness was evaluated. Plasma nitriding was carried out in order to evaluate the nitriding behaviour of the surfaces modified by EB. Applying the EB meander technique results in smooth surfaces, good microstructural connection to the matrix material and a homogeneous distribution of the alloying elements together with an increase in hardness of ～300 HV0·1. Plasma nitriding leads to the formation of AlN layers of ～5 μm thickness.     

Microstructure and properties of semisolid hypereutectic high chromium cast iron prepared by slope cooling body method

Abstract

To improve the toughness of hypereutectic high chromium cast iron, the morphology of the primary carbides were improved by the slope cooling body method, a semisolid forming process. The semisolid specimens were prepared under different forming techniques, and the microstructure, impact toughness and wear resistance were studied. The results indicate that the morphology of primary carbide is improved, impact toughness initially increases then remains constant as the semisolid forming temperature increases, impact toughness was improved, but wear resistance was reduced.     

22—A THEORETICAL AND EXPERIMENTAL INVESTIGATION OF THE CREASE RECOVERY OF PLAIN-WEAVE FABRICS WOVEN FROM STAPLE YARNS

The retained angle at a crease is considered to be made up of two components: inelastic and frictional. A theoretical scheme has been developed that enables the inelastic component to be calculated from the appropriate fibre, yarn and fabric data and the calculations are illustrated for three fabrics.

An experimental investigation of the crease-recovery behaviour of these fabrics, in conjunction with the calculations described above, has established a method of deducing the frictional component from the low-curvature bending-recovery behaviour of a fabric, and it is thus possible to make an estimate of the fabric crease-recovery angle. The calculation has been carried out for a range of fabrics woven from eighteen fibre types, each in four different cover factors, and the results are shown to agree reasonably well with the measured crease-recovery angles for the same fabrics. The experimental results are discussed and some interesting relationships are pointed out; in particular it is shown that fabrics must be well relaxed if the full potential of a high-recovery fibre is to be realized.     

Preparation and tribological properties of carbon fibre reinforced poly(vinylidene fluoride) composites

Abstract

The current study examines the tribological performance of poly(vinylidene fluoride) (PVDF) and carbon fibre reinforced poly(vinylidene fluoride) (CF/PVDF) under dry sliding condition. Different contents of carbon fibres (CFs) were employed as reinforcement. All filled and unfilled polyimide composites were tested against CGr15 ball and representative testing was performed. The effects of CF content on tribological properties of the composites were investigated. The worn surface morphologies of neat PVDF and its composites were examined by scanning electron microscopy and the wear mechanisms were discussed. Moreover, all filled PVDFs have superior tribological characteristics to unfilled PVDFs. The optimum wear reduction was obtained when the content of CF is 20 vol.-%.     

Hard amorphous nanocomposite coatings with oxidation resistance above 1000°C

Abstract

This article reports on two classes of novel hard amorphous coatings: (a) Si₃N₄/MeN_x coatings with high (≥50 vol.-%) content of Si₃N₄ phase; here Me=Zr, Ta, Ti, Mo, W, etc. and x=N/Me is the stoichiometry of MeN_x metal nitride phase, and (b) Si–B–C–N coatings with strong covalent bonds. These nanocomposites exhibit high thermal stability against crystallisation and high oxidation resistance, both at temperatures considerably exceeding 1000°C. Hard amorphous coatings were prepared using reactive magnetron sputtering. Properties of sputtered coatings were characterised using the following techniques: X-ray diffraction, electron probe microanalysis, Rutherford backscattering spectrometry, elastic recoil detection, high resolution transmission electron microscopy, selected area electron diffraction, atomic force microscopy, microhardness tester Fischerscope H 100, differential scanning calorimetry and thermogravimetric analysis. It was found that hard amorphous coatings of both new systems exhibit excellent oxidation resistance at high temperatures about 1500 and 1700°C for amorphous Si₃N₄/MeN_x and Si–B–C–N coatings respectively.     

Physico-chemical Causes of the Extent of Water Resistance of Linearly Welded Wood Joints

A change in linear welding conditions, namely higher vibration frequency (150 Hz) and lower displacement (2 mm) during welding, produced a quicker rise in temperature of the weldline. This allowed a much shorter welding time (1.5 s). X-ray microdensitometry mapping showed a progressive increase in broadening and average density of the weldline as the welding time lengthens. As the welding time lengthens the maximum temperature reached at the end of welding is progressively higher. This causes increasingly greater degradation. This effect was confirmed also by CP-MAS ¹³C NMR and it was found that the lower is the degree of deterioration of the weldline of the wood joint the shorter is the welding time. Monitoring of the temperature of the weldline showed that the temperature reached in wood joints during welding was inversely correlated to its water resistance. Furthermore, the increase in weldline temperature is markedly quicker at a vibration frequency of 150 Hz than at 100 Hz. Thus, the shorter is the welding time the lower is the degree of deterioration of the weldline of the wood joint. This appears to be due to welding occuring when water vapour is still present in the joint, hence providing a less damaging welding environment.