Removal of heat-formed coating from a titanium alloy using high pressure waterjet: Influence of machining parameters on surface texture and residual stress

Abstract

Citation: HUANG, L., KINNELL, P. and SHIPWAY, P.H., 2015. Removal of heat-formed coating from a titanium alloy using high pressure waterjet: Influence of machining parameters on surface texture and residual stress. Journal of Materials Processing Technology, 223, Additional Information:• This paper was accepted for publication in the journal Journal of Materials AbstractTitanium alloys are widely used in aerospace and medical industries owing to high strength to weight ratio and outstanding corrosion resistance. A problem for titanium or titanium alloys is the existence of a hard, brittle and oxygen-enriched layer on the surface (so called alpha case) which is usually formed during hot forming processes or after long-term service at elevated temperatures in an open-air environment. With the development of waterjet system, high pressure waterjet has shown its capability for the removal of such hard and difficult-tomachine coatings. Waterjet machining is usually associated with a surface roughening effect due to the repetitive impacts of droplets. Surface roughening is unwanted for most of aerospace applications as rough surface is detrimental to the fatigue behavior of components, but is beneficial for medical application where fixation is required (e.g. metal orthopedic implants). An additional benefit of waterjet material removal is that the repetitive droplet impacts may introduce compressive residual stress to the machined surface and subsurface layers. In this study, Ti-6Al-4V with alpha case layer was subjected to plain waterjet over a range of parametric conditions. The completeness of alpha case removal was characterized by the depth of removal. The textured surfaces were quantified in terms of average surface roughness (Ra) and apparent volume for interdigitation (V i ). The magnitude of residual stress of PWJ-machined surfaces was measured using X-ray diffraction (XRD). ANOVA analysis was also conducted to identify the relative significance of machining parameters to the process outputs. It was found that an increase in removal depth results in an increase in the surface roughness as well as the interdigitation volume regardless of machining conditions. A compressive residual stress (-563 MPa~ -13 MPa) was found within all PWJ-machined surfaces. It was concluded that a maximum compressive residual stress simultaneous to a

Multi-scale characterization of material and surface integrity of Inconel 718 when milling by Abrasive Water Jet process: Context of repair application

“…This can be explained by the fact that an increase in traverse speed leads to a decrease in exposure time which generates less work-hardening with lower residual stresses. This trend of exposure time on residual stresses was observed in titanium alloy impacted by plain waterjet [29].…”

A Critical Review on Effects of Residual Stresses on Machining of Titanium alloys by various Non-Conventional Processes

“…The authors also noted that for AWJ peening under the same conditions, residual stresses within cpTi were lower than those within Ti-6Al-4V, whereas for WJ peening under the same conditions, residual stresses within cpTi were greater than those within Ti-6Al-4V. In a study by Huang et al [28], the authors subjected Ti-6Al-4V alloy with a brittle, hard and oxygen-enriched surface layer to a plain jet of water over a range of parametric conditions. The magnitude of the residual stress of PWJ-machined surfaces was measured using X-ray diffraction.…”

“…While residual compressive stresses inhibit the growth of fatigue cracks, the growth is generally compounded in the presence of residual tensile stresses [4]. Some well-known methods for developing compressive residual stresses are shot peening, laser peening, waterjet peening, abrasive finishing, and cold rolling [5]. Residual stresses have other negative effects also as they can decrease both the static and dynamic strength, decrease the resistance to corrosion, cause dimensional instability (distortion of the component), cause magnetic properties to change, etc.…”

Strength, fatigue strength and toughness of dissimilar Ti17–Ti64 linear friction welded joints: Effect of soft surface contamination and depletion of α precipitates

“…The high content in O and the grains morphology of the defect layer suggest that it might be an oxide layer. Another plausible interpretation is that the defect layer may have favoured the diffusion of the others elements [49] and have induced the formation of a brittle phase known as α-case [50]. Below, it will be shown that the defect layer is very detrimental for the mechanical properties and that it can be easily avoided by a proper prior to welding surface preparation.…”