Friction Welding and description of zones Quality requirements of welded joints depend on the form of application, e.g. in the space or fly industry weld errors are not allowed. There are many scientific articles describing the weld, weld quality tests assurance is performed, with measurements and numerical methods. Science tries to gets good quality welds. For example, an ultra fine grain structure of alloy or metal which is obtained by techniques such as severe plastic deformation is desirable, and not changed by the high temperature, a large heat affected zone is unnecessary. Moreover, in addition to changing the grain structure during metal joining cycles, by methods where high temperature affected zone was occur, are phase transformations structure. For example, in steel between austenite, ferrite, pearlite, bainite, cementite and martensite, see: Iron-carbon phase diagram. In order to avoid changes solid state welding may be desired and large heat affected zone is not needed if weakens the material properties. Heat and mechanical affected zones in friction weld Individual thermomechanical zones can be described by citing an example article: Anthony R.McAndrew, Paul A.Colegrove, Clement Bühr, Bertrand C.D., Flipo Achilleas Vairis, "A literature review of Ti-6Al-4V linear friction welding", 2018. "Technically the WCZ and the TMAZ are both "thermo-mechanically affected zones" but due to the vastly different microstructures they possess they are often considered separately. The WCZ experiences significant dynamic recrystallisation (DRX), the TMAZ does not. The material in HAZ is not deformed mechanically but is affected by the heat. The region from one TMAZ/HAZ boundary to the other is often referred to as the "TMAZ thickness" or the plastically affected zone (PAZ). For the remainder of this article this region will be referred to as the PAZ." Zones: WCZ– weld center zone, HAZ – heat affected zone, TMAZ – Thermo-Mechanically Affected Zone, BM – base material, parent material, Flash. Similar terms exist in welding. Seizure resistance Friction welding may unintentionally occur at sliding surfaces like bearings. This happens in particular if the lubricating oil film between sliding surfaces becomes thinner than the surface roughness, which may be due to low speed, low temperature, oil starvation, excessive clearance, low viscosity of the oil, high roughness of the surfaces, or a combination thereof. The seizure resistance is the ability of a material to resist friction welding. It is a fundamental property of bearing surfaces and in general of sliding surfaces under load. Curiosities Frictional welding