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Wear
Published in Ahmed Abdelbary, Extreme Tribology, 2020
Galling is a severe form of adhesive wear that occurs when unlubricated, metallic or ceramic, surfaces are compressed against one another, at a slow speed. When the compressive forces in conjunction with the forces causing the sliding motion are sufficient, friction creates heat sufficient to weld the materials together. This unintentionally removes material from one material and places it onto the other one. In general, the main factors affecting galling are: design, applied load, contact area and degree of movement, lubrication and environment, and material properties (surface finish, hardness and steel microstructure).
Joint Failure
Published in John H. Bickford, An Introduction to the Design and Bchavior of Bolted Joints, 2018
Galling is a cold welding process which occurs when the surfaces of male and female threads come in such close contact that an atomic bond can form between them. Galling is encouraged by such things as lack of lubrication, lack of oxide film on the metal, high contact pressure, and heat. Stainless steel bolts are particularly likely to gall.
Lubrication Overview – Chemical Aspect
Published in Kenneth C. Ludema, Oyelayo O. Ajayi, Friction, Wear, Lubrication, 2018
Kenneth C. Ludema, Oyelayo O. Ajayi
Because different terminologies are used by various disciplines engaged in the study of marginal lubrication, several conventional terms require definition: 1.The chemical effects in lubrication are referred to as boundary lubrication and defined more fully in following sections.2.The catastrophic mode of surface failure is sometimes referred to as scuffing or scoring, or perhaps galling or seizing. Many of these terms are old, poorly understood, and apply principally to ductile metals. Each of these terms has several technical (and subjective) meanings, and each describes different end results. In the interest of reducing the number of terms to be used in this chapter some definitions will be proposed.Seizing is a term that describes such severe damage of sliding surfaces that the driving system cannot provide sufficient force to overcome friction: the sliding pairs cease to slide.Galling is a process of surface roughening that results from high contact pressure and high traction, at slow speed generally and without any lubricant other than the native oxide and adsorbed gas on the surfaces. Most likely the failure of lubricated surfaces within the first few cycles of contact is similar to the galling process but failure at a later stage is different.Scuffing and scoring by contrast usually refer to a mode of failure of well-lubricated metal parts. Subjectively they are described as different from galling and seizing, but the initiating mechanism of all may be the same.Surfaces that are said to have scuffed have become so rough that they no longer provide their expected function. They may or may not have worn away to any great extent. From this point of view, scuffing is not a wearing mechanism, but primarily a surface roughening mechanism. Scuffed surfaces have a range of characteristic appearances. Some are shiny, some have grooves in them, and some are dull, probably depending on the chemical environment in which they operate.Scoring is a parallel phenomenon, sometime manifested as a dull-appearing surface with no obvious roughening. Scored surfaces may only display evidence of overheating of either a lubricant or the metal.3.Break-in refers to the action taken to prepare sliding surfaces for high load-carrying capacity (LCC). Generally, new surfaces cannot carry high loads without failure.
Optimisation of cutting parameters for machining of newly developed Co-free hard-faced nuclear reactor components
Published in International Journal of Ambient Energy, 2021
Manchukonda Tarun, Chitturi Naga Sai Kumar, A. Vidya Sagar Patro, N. Beemkumar
India envisages a three-stage programme for nuclear power generation. In the first stage, power is generated by pressurised heavy water reactor with natural UO2 as the fuel matrix and India achieved complete self-reliance in this technology and this stage of the programme is in the industrial domain. India’s second stage of nuclear power generation envisages the use of Pu-239 obtained from the first-stage reactor operation, as the fuel core in fast breeder reactors and this stage of the programme is being adapted to the industrial domain. The third phase of India’s nuclear power generation programme is breeder reactors using U-233 fuel and it is in the development stage. The components of fast breeder reactor require high-temperature strength (Bendorf 1970); wear resistance and corrosion resistance properties at elevated temperatures. Structural material AISI 316L (N) does not have adequate high-temperature tribological properties. Hence, the use of hard-faced coating on these structural materials is required to avoid galling at high temperature (Britto Joseph et al. 2018; Kalyan Das and Sahoo 2011). The use of cobalt-based alloy is abandoned in nuclear industries due to induced radioactivity from Co60 in the reactor environment. Hence, Nickel-based Tribaloy 700 hard-facing alloy has been chosen to improve surface properties of structural material. Hardness of the alloy is derived from hard carbides, borides embedded in austenite matrix. In nuclear reactor applications, the use of cobalt-based alloys leads to induced activity from Co60 isotope formed in the nuclear reactor environment. Hence, the nickel- based hard-facing alloys of hardness 58–65 HRC have been developed to replace the cobalt-based hard-facing alloys. Tribaloy 700 is basically a nickel- based alloy and the hardness of the deposited weld metal is 58–65 HRC. Various cutting tools are available for normal machining like high speed steel, Stellite, Tungsten carbide, ceramic, coated inserts, cermets, cubic boron nitride (CBN) inserts and Diamond (Neeraj et al. 2014; Suresh and Krishnaiah 2013). Among these which tool is to be used for easy machining of Tribaloy 700 for achieving superior surface finish is discussed here. This project deals with selection of cutting tools, machining steps, selection of cutting speed, selection of feed, depth of cut for easy machining with superior surface finish of Tribaloy 700 hard-faced precision nuclear components.