Papers by Keyword: Hardness

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Authors: Tian Bo Yu, Niels Hansen
Abstract: A model is suggested to analyze recovery kinetics of heavily deformed aluminum. The model is based on the hardness of isothermal annealed samples before recrystallization takes place, and it can be extrapolated to longer annealing times to factor out the recrystallization component of the hardness for conditions where recovery and recrystallization overlap. The model is applied to the isothermal recovery at temperatures between 140 and 220°C of commercial purity aluminum deformed to true strain 5.5. EBSD measurements have been carried out to detect the onset of discontinuous recrystallization. Furthermore, comparison between the present model and a similar recently developed recovery model is made, and the result is discussed.
Authors: Xiang Tian Chen, Ye Han, Shu Yu Yao, Wei Wei Zhang, Yun Sui Yao, Zong Feng Wang
Abstract: A new glass-ceramic coating material on nickel based super alloy substrate had been found, the glass¬-ceramic coating material was developed from a glass based on MgO–Al2O3–TiO2 system. The coating material was characterized through X-ray diffractometry (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), hardness, thermal expansion coefficient testing. XRD analysis of the coating materials and the resultant coatings showed presence of a number of microcrystalline phases. SEM micrographs indicated microstructure of the material. Optical micrographs showed smooth glossy impervious free surface with defects. Hardness analysis showed the glass-ceramic coating material had higher microhardness. The thermal expansion coefficient of the nimonic alloy was much higher compared to the coating material at specific temperature.
Authors: Qian Bai, Jian Guo Lin, Gao Feng Tian, Daniel S. Balint, Jin Wen Zou
Abstract: Powder metallurgy (PM) of nickel-based superalloys has been used for a wide range of products owing to their excellent special properties in processing and applications. Typical processes for high performance PM superalloys include hot isostatic pressing, hot extrusion and hot isothermal forging. Hot isostatic pressing is normally conducted at a high temperature, by using a low pressure for a long time in a closed vessel, resulting in high cost and low product efficiency. In this paper a novel forming process, i.e. direct powder forging for powder metallurgy of superalloys has been proposed. In this process, the encapsulated and vacuumed powder is heated up to the forming temperature and forged directly to the final shape, by using a high forming load for a very short time. Direct powder forging is a low-cost and energy-saving process compared to conventional PM processes, and in addition, press machines of conventional forging can be used for direct powder forming process. In direct powder forging it is important to control the relative density of the deformed part since the existence of voids could reduce the mechanical strength and fatigue life. In this paper, feasibility tests of direct powder forging are presented. Microstructure, relative density and hardness of the formed specimen were studied.
Authors: Alexander G. Ovcharenko, Andrey Yu. Kozlyuk, Mikhail O. Kurepin
Abstract: Abstract. A promising method for improving wear resistance of metal cutting tools including pre-heating and a subsequent impact of the pulsed magnetic field of high intensity on the cutting tool is proposed. The experimental setup and methods of research are described. Experimental studies of surfaces of carbide reversible cutting plates of the VK8, T15K6 alloy and drills of high speed steel R6M5 to assess the effectiveness of the proposed method were performed. An increase in wear resistance of cutting tools made of the T15K6 hard-alloy plates by 30% and made of the VK8 alloy plates by 13% was revealed while wear resistance of drills made of steel R6M5 increased on average by 58% The proposed method can be of practical interest for hardening the surface of other types of tools and machine parts for further experimental verification.
Authors: Chih Ling Lin, Han Huang, Bronwen W. Cribb, Anthony Russell
Abstract: Human bone fracture associated with osteoporosis was hypothesized to be related to the alteration of mechanical properties in bones. In this work, cortical and trabecular bones from human femoral heads were studied. Bone samples of eight female and four male patients, with ages varying from 37 to 93 years, were collected from total hip replacement surgery. Reduced modulus (Er) and hardness (H) of osteons, interstitial lamellae and trabeculae were characterized by nanoindentation. The results showed both the reduced modulus and hardness of the interstitial lamellae were significant higher than those of osteons and trabeculae. Though there was no significant difference in microstructures in the Group A (age < 60 years) and B (age > 60 years), the Group B bones demonstrated to be stiffer.
Authors: Mehdi Soodi, Milan Brandt, Syed H. Masood
Abstract: This paper presents an investigation on the microstructure and surface hardness of the parts fabricated by laser assisted Direct Metal Deposition (DMD) technology. A series of engineering metallic alloy powders were used in the DMD process to produce simple 3D geometric structures. The alloy powders investigated include: 316L stainless steel, 420 Stainless Steel, Stellite(R) 6, tool steel (H13), Cholmoloy (Ni Based alloy), and Aluminium Bronze. These were chosen due to their frequent application in engineering parts and components. The microstructure and hardness values have been compared to those of the wrought products (as annealed) as reported in the SAE standards, Heat treater’s guide to metals ASM international, and material data sheets supplied by the materials manufacturers. A significant difference is reported in both hardness and microstructure of the laser deposited samples compared to those of the wrought form.
Authors: Usman Sudjadi
Abstract: A study of surface hardening on local bolts (C=0.01%) at a temperature of 400°C for 5 and 6 hours with nitrocarburizing using RF-plasma apparatus. The objective of this experiment was to seek a surface material of local bolts that is more resistant to friction and having better surface uniformity, higher hardness and higher corrosion resistance. The experiment was conducted on the local bolts (C = 0.01%) with a radio-frequency (RF) plasma nitrocarburizing equipment. The nitrocarburization was done on the local bolts at a temperature of 400°C, with a variation of nitrocarburizing times of 5 and 6 hours. The results showed that the average hardness of local bolt samples before nitrocarburization was 136.08 kgf/mm2. After nitrocarburization at a temperature of 400°C for 5 hours, the average hardness of local bolt samples was 199.1 kgf/mm2. After nitrocarburization at a temperature of 400°C for 6 hours, the average hardness of local bolt samples was 201.12 kgf/mm2. The matrixes on the base material were ferrite, austenite, and pearlite.
Authors: T.V.K. Gupta, J. Ramkumar, Puneet Tandon, N.S. Vyas
Abstract: The current trend in abrasive water jet machining process is getting focused on milling applications using this technique. Abrasive water jet machining (AWJM) process is a well defined process for cutting or part separation. The present paper reports on the geometry obtained in controlled depth milling process of different materials. The dimensions considered in this paper are the pocket depth and the change in the kerf profile. Experimental observations are made relating the kerf profile with traverse speed and the mechanical properties of the work piece material. Tool paths for obtaining the pocket of size 9 mm x 20 mm are generated in raster mode and machined using AWJM on materials of varying hardness and at different traverse speeds. It is observed that there is a significant change in the geometry of the kerf profile and also the depth of the pocket with speed in conjuction with the material hardness.
Authors: Lorella Ceschini, Alessandro Morri, Fabio Rotundo, Tea Sung Jun, Alexander M. Korsunsky
Abstract: The aim of the present work is to evaluate the possibility of using the Linear Friction Welding (LFW) technique to produce similar and dissimilar joints between a 2024 Al alloy and a 2124Al/25vol.%SiCP composite. In this solid state joining process the bonding of two flat edged components is achieved through frictional heating induced by their relative reciprocating motion, under an axial compressive force. Microstructural characterization of the welds was carried out by optical and scanning electron microscopy, to investigate the effect of LFW both on the aluminium alloy matrix and the reinforcement particles. The mechanical behaviour of the welded specimens was studied by means of hardness and tensile tests. The mechanisms of failure were investigated by SEM analyses of the fracture surfaces. LFW joints in MMCs resulted substantially defect free, with a uniform particle distribution, while a partial lack of bonding at the corners was observed in the others welds. The hardness decreased by approximately 10% in the welded zone, with some data fluctuations due to the complex microstructural modifications introduced by the LFW process. The joint efficiency, evaluated in respect to the UTS, was 90% for the Al alloy joints and 80% for the MMC joints. A decrease in the elongation to failure was measured in all the LFW specimens, probably related to the orientation of the plastic flow in the TMAZ, where the fracture generally occurred.
Authors: Nasuha Sa'ude, Mustaffa Ibrahim, Ibrahim Raman
Abstract: This paper presents the development of a new polymer-ceramic composite material for use in injection molding machine. The material consists of palm oil fly ash (POFA) in a high density polyethylene (HDPE) powder. In this study, the effect of POFA was investigated as a filler material in polymer-ceramic matrix composite and HDPE was chosen as a matrix material. The detailed formulations of mixing ratio with various combinations of the new polymer-ceramic composite are investigated experimentally. Based on the result obtained, it was found that, the weight percentage increment of POFA filler affected the flexural and hardness strength. This work represents a major development in recycling of waste material from palm oil empty fruit bunch out of the refinery to produce polymer/ceramic matrix composite.
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