Vol.58, No. 5 - Indira Gandhi Centre for Atomic Research

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Trans. Indian Inst. Met. Vol.58, No. 5, October 2005, pp. 911-929 REVIEW FRETTING FATIGUE OF BIOMATERIALS 1 Aravind Vadiraj, 1 M. Kamaraj, 2 U. Kamachi Mudali and 2 Baldev Raj 1 Department of Metallurgical and Material Engineering, Indian Institute of Technology Madras, Chennai – 600036, India 2 Indira Gandhi Center for Atomic Research, Kalpakkam 603102, India (Received 28 February 2005 ; in revised form 13 April 2005) ABSTRACT The use of metals and materials for replacement and repair of human body parts are attracting more attention in recent times. Like any other components in service, biomaterials also undergo degradation due to fretting, wear and corrosion. Fretting wear, fretting fatigue and fretting corrosion are the three main areas of concern for the orthopedic surgeons. This paper reviews fretting fatigue along with various methodologies and mechanisms. Fretting of materials is controlled by several sets of variables working synergistically, making the process difficult to quantify. A fretting test rig for biomaterials has been developed simulating the conditions of the actual implants as close as possible. Fretting fatigue life is also controlled by contact geometries, which delay or accelerate the crack initiation. Several contact geometries have been mentioned which can influence the fretting life of the materials. Fretting conditions are also governed by normal pressure and slip amplitude regime in fretting maps. Physiological medium may aggravate or reduce the fretting failures depending on the nature of surface and the medium. Titanium alloys have been established as the most suitable materials for bio implants due to their attractive properties within the body environment. Some important aspects of the fretting damage of these alloys are mentioned in this paper. Fretting fatigue life of these alloys can be significantly improved by surface modification with specialized techniques such as plasma nitriding, ion implantation and Physical Vapour Deposited TiN coatings. The paper describes details of these methods as well. Trans. Indian Inst. Met. Vol.58, No. 5, October 2005, pp. 931-937 REVIEW IMPURITIES IN ALUMINIUM ALLOYS - CHALLENGES FOR AEROSPACE QUALITY: A REVIEW R.K. Gupta, R. Panda, B.R. Ghosh and P.P. Sinha Mechanical Engineering Entity, Vikram Sarabhai Space Centre, Trivandrum-22 E-mail : rohitkumar_gupta@vssc.org (Received 9 March 2005 ; in revised form 19 June 2005) ABSTRACT The quality of cast billets of aluminium alloys essentially dictates their behaviour during further downstream processing for fabrication of hardwares and their performance in service. The stringent design criteria demanded by launch vehicle applications cannot be met without controlling various detrimental factors of material, like presence of impurities and trace elements including alkali metals, non metallic inclusions, gas contents etc. during melting stage itself. A general review of the effects of these harmful elements and their control are presented in this paper. A very rational approach to sort out these problems is also suggested.
Trans. Indian Inst. Met. Vol.58, No. 5, October 2005, pp. 801-808 TP 2001 KINETICS AND MECHANISM OF IRON ORE – COAL COMPOSITE PELLETS REDUCTION S.K. Dutta Metallurgical Engineering Department, Faculty of Tech. & Engg., M. S. University of Baroda, Kalabhavan, Vadodara 390 001. E Mail: skdmet@yahoo.com (Received 18 October 2004 ; in revised form 15 February 2005) ABSTRACT Composite pellet contains mixture of fines of iron bearing oxide and carbonaceous material (coal, coke etc), which has been imparted sufficient green strength for subsequent handling by cold bonding technique. The composite pellets offer the advantage of reduction rate, utilization of fines and pollution control. During non-isothermal reduction of composite pellets, it is found that degree of reduction varies from 46 to 99 pct, depending upon pellets composition and heating rate. It is also observed that devolatilization of coal generates reducing gases (such as H 2 , CO etc). A significant quantity (approximately 10 to 20 pct of pellet weight) of extraneous H 2 O and CO 2 are retained by oven-dried pellets as chemically combined or strongly adsorbed species. These gases, liberate during heating to high temperature, react with carbon and hydrocarbon to generate additional quantities of CO and H 2 . The paper analyses the non-isothermal kinetics data and discusses the mechanism of iron ore – coal composite pellets reduction. Activation energy values obtained for final stage reduction, vary from 183 to 268 KJ/ mol. Hence, it can be concluded that the overall rate of reduction of composite pellets is controlled by the rate of gasification reactions.
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Vol.58, No. 5 - Indira Gandhi Centre for Atomic Research

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