EFFECTS OF TIN ON HARDNESS, WEAR RATE AND COEFFICIENT OF FRICTION OF CAST CU-NI-SN ALLOYS

An investigation was carried out to understand the effects of Sn on hardness, wear rate and the coefficient of friction of spinodal Cu-Ni-Sn alloys. Alloys of appropriate compositions were melted in a crucible furnace under argon atmosphere and cast into sand moulds. Solution heat treated and aged specimens were tested for hardness, wear rate and the coefficient of friction. It was found that the hardness increases when the Sn content increases from 4% to 8% in the solution heat treated conditions. The peak aging time is found to decrease with an increase in the Sn content. Further, the coefficient of friction is independent of hardness whereas the wear rate decreases linearly with hardness irrespective of Sn content

Distinct evolutionary origins of intron retention splicing events in NHX1 antiporter transcripts relate to sequence specific distinctions in Oryza species

The genome of Asian cultivated rice (Oryza sativa L.) shows the presence of six organelle-specific and one plasma membrane (OsNHX1-7) NHX-type cation proton antiporters. Of these, vacuolar-localized OsNHX1 is extensively characterized. The genus Oryza consists of 27 species and 11 genome-types, with cultivated rice, diploid O. sativa, having an AA-type genome. Oryza NHX1 orthologous regions (gene organization, 5′ upstream cis elements, amino acid residues/motifs) from closely related Oryza AA genomes cluster distinctly from NHX1 regions from more ancestral Oryza BB, FF and KKLL genomes. These sequence-specific distinctions also extend to two separate intron retention (IR) events involving Oryza NHX1 transcripts that occur at the 5′ and 3′ ends of the NHX1 transcripts. We demonstrate that the IR event involving the 5′ UTR is present only in more recently evolved Oryza AA genomes while the IR event governing retention of the 13th intron of Oryza NHX1 (terminal intron) is more ancient in origin, also occurring in halophytic wild rice, Oryza coarctata (KKLL). We also report presence of a retro-copy of the OcNHX1 cDNA in the genome of O. coarctata (rOcNHX1). Preferential species and tissue specific up- or down-regulation of the correctly spliced NHX1 transcript/5′ UTR/13th intron-retaining splice variants under salinity was observed. The implications of IR on NHX1 mRNA stability and ORF diversity in Oryza spp. is discussed

Delayed Effects of Acute Radiation Exposure in a Murine Model of the H-ARS: Multiple-Organ Injury Consequent to <10 Gy Total Body Irradiation

The threat of radiation exposure from warfare or radiation accidents raises the need for appropriate animal models to study the acute and chronic effects of high dose rate radiation exposure. The goal of this study was to assess the late development of fibrosis in multiple organs (kidney, heart, and lung) in survivors of the C57BL/6 mouse model of the hematopoietic-acute radiation syndrome (H-ARS). Separate groups of mice for histological and functional studies were exposed to a single uniform total body dose between 8.53 and 8.72 Gy of gamma radiation from a Cs radiation source and studied 1-21 mo later. Blood urea nitrogen levels were elevated significantly in the irradiated mice at 9 and 21 mo (from ∼22 to 34 ± 3.8 and 69 ± 6.0 mg dL, p < 0.01 vs. non-irradiated controls) and correlated with glomerosclerosis (29 ± 1.8% vs. 64 ± 9.7% of total glomeruli, p < 0.01 vs. non-irradiated controls). Glomerular tubularization and hypertrophy and tubular atrophy were also observed at 21 mo post-total body irradiation (TBI). An increase in interstitial, perivascular, pericardial and peribronchial fibrosis/collagen deposition was observed from ∼9-21 mo post-TBI in kidney, heart, and lung of irradiated mice relative to age-matched controls. Echocardiography suggested decreased ventricular volumes with a compensatory increase in the left ventricular ejection fraction. The results indicate that significant delayed effects of acute radiation exposure occur in kidney, heart, and lung in survivors of the murine H-ARS TBI model, which mirrors pathology detected in larger species and humans at higher radiation doses focused on specific organs

Determination of the Effect of Si Content on Microstructure, Hardness and Wear Rate of Surface-refined Al-Si Alloys

AbstractSurface refining of Al–Si alloy was carried out using the ‘Gas Tungsten Arc’ (GTA) heat source and the effect of Si content on the microstructure, hardness and wear properties of the surface modified alloys was evaluated. In order to further improve its wear resistance, the Surface Refining Process (SRP) was employed in this study. In the SRP, the surface of the parent material is melted by a suitable heat source and the molten zone is allowed to solidify progressively. It can be noted from the literature that e-beam and laser are the only heat sources employed. Both these sources are highly expensive and their productivity is also low. The depth of the modified layer by e-beam or laser process is found to be inadequate for wear applications. In order to overcome the above shortcomings, in this study, the surface refining of Al–Si alloy was carried out by using an inexpensive, high productivity and commonly available GTA source. In this work, the effect of Si content on the properties is evaluated by varying the Si content from 4-16 wt%. The alloys were sand–cast in the form of bar(150x30x30mm). The Surface melting was carried out with the following GTA parameters: current-150 A, travel Speed-2mm/s, arc length-3mm, tip angle-1800 and electrode diameter-2.4mm. The hardness was measured at different locations by using Vickers Hardness Tester by applying 100 gm load for 15 s and an average value was taken. The wear testing was conducted as per ASTM G99 standard under a dry sliding condition in air using Pin–on–Disc wear tester. In this study, it was noted that the typical as–cast microstructure of the Al–Si alloy illustrating the elongated morphology of the eutectic–Si has been completely refined, and the eutectic–Si is finely dispersed within the α–Al matrix. It is inferred that the microstructure was refined due to fast cooling to have a globular eutectic–Si dispersed within a fine–grained matrix in the GTA process. It was found that the depth of the modified layer is significantly higher than that obtained in the e-beam/laser process. The hardness of the modified layer was found to increase when the Si content is increased from 4-16 wt%. The wear rate is found to decrease with an increase in the Si content whereas the coefficient of friction tends to remain the same. The wear mechanism was found to be adhesive. Finally, the peak hardness of the modified layer increased significantly upon ageing. The observations are in agreement with that of previous studies

MEASUREMENT OF THE VARIATION OF MECHANICAL PROPERTIES WITH AGING TEMPERATURES FOR SAND CAST Cu-5Ni-5Sn ALLOY

The purpose of the investigation is to study the mechanical properties of copper-nickel-tin spinodal alloy and its effect with respect to aging temperatures using sand casting process without cold work. An alloy of Cu-5Ni-5Sn was melted in a crucible furnace under argon atmosphere and cast into sand moulds. Homogenized and solution treated specimens were aged at 300 °C, 350 °C, and 400 °C for different period of time. Specimens were tested for its mechanical properties such as micro-hardness, yield stress, tensile stress and percent elongation. It was found that the peak hardness increases with aging temperatures up to 400 °C. Yield and tensile stresses are proportional to hardness of the alloy. Percent elongation decreases with increase in hardness and stresses. Incremental yield stress increases with increase in aging temperature of the alloy. Also, the yield stress of the alloy is found to increase two times than that of traditional cast bronze alloys

Study of hardness and wear behavior of surface modified AA 7075 with tungsten carbide using GTA as a heat source

233-242The aim of this work is to evaluate the role of tungsten carbide (WC) in increasing the hardness and improving the wear resistance of AA 7075 alloy. WC is reinforced into the surface of AA 7075 by using gas tungsten arc (GTA) as a heat source. Some of the GTA process parameters are maintained as constant, viz, contact-to-work distance and electrode tip angle, whereas the heat source current and the work speed are varied. With reference to the proper fusion of base metal, optimum GTA heat source parameter is finalized based on a number of trials. It is found that the hardness is reduced after the application of heat. To improve the properties, the alloy is subjected to heat treatment which included solution treatment, water quenching, and artificial aging. The hardness and wear behavior of the WC reinforced surface composite resulted in a positive trend. A comprehensive study on the microstructure of AA 7075 at different stages of the work is done using optical microscopy (OM), scanning electron microscopy (SEM), EDX analysis and X-ray diffraction (XRD)