November/December AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 1 8 4 8 iTSSe TSS iTSSe TSS DETERMINATION OF TRIAXIAL RESIDUAL STRESS IN PLASMA-SPRAYED HYDROXYAPATITE (HAP) DEPOSITED ON TITANIUM SUBSTRATE BY X-RAY DIFFRACTION N. Bosh, H. Mozaffari-Jovein, and C. Müller Measurement of residual stress in plasma-sprayed coat- ings is of key importance to optimize their microstructure and mechanical properties. In this study, x-ray diffraction anal- ysis was carried out using the sin 2 ψ method to evaluate the residual stress distribution of hydroxyapatite (HAp) coatings produced on a titanium substrate by atmospheric plasma spraying (APS) and vacuum plasma spraying (VPS). The sin 2 ψ method measured strains at different tilt ψ and rotating φ an- gles around the specimen surface normal. A nonuniform and inhomogeneous stress distribution was present in both coat- ings. Themeasured strain εψφ is plotted versus sin 2 ψ , showing a nonlinear (elliptical) behavior, which indicates the presence of inhomogeneous triaxial stress distributions within the coat- ings due to the crystalline anisotropy, inhomogeneous cooling rate, or solidification of molten particles. The normal stress values within both HAp coatings were found to be tensile in nature, but the tensile stress values are significantly higher in the APS coating versus the VPS coating (Fig. 3). PREDICTING THE LOAD-CARRYING CAPACITY AND WEAR RESISTANCE OF DUPLEX-COATED LOW-STRENGTH ALLOYS FOR SEVERE SERVICE BALL VALVES M. Laberge, E. Bousser, J. Schmitt, M. Koshigan, T. Schmitt, F. Khelfaoui, S. Isbitsky, L. Vernhes, and J. E. Klemberg- Sapieha The load-carrying capacity and wear resistance of a du- plex-coated 316 stainless steel were determined, and a finite element numerical approach was developed to predict and corroborate experimental observations. Low-strength alloys are generally used for highly demanding valve applications due to their superior chemical stability, galvanic corrosion resistance, and lower susceptibility to stress corrosion crack- ing failure. Hardfacing (using thermal spray, laser cladding, or plasma transferred arcwelding) is currently themost common solution to protect valve components. Hardfacing provides a thick, hardened case that significantly improves tribological performance. However, hardfaced layers provide lower wear resistance compared to vacuum-deposited hard coatings. One solution to further improve hardfacing performance is a du- plex approach, which combines the two processes. This study investigates the following materials: a 316 stainless steel base hardfaced with laser-cladded Co-Cr superalloy and topped with a CVD nanostructured W-WC coating. Tribological prop- erties of three configurations were assessed for their ability to delay initiation of plastic deformation and surface cracking under quasistatic loading and for their resistance to dry recip- rocal sliding wear. The results demonstrate that finite element modeling allows numerical prediction and comparison of the load-carrying capacity and wear resistance of duplex-coated AISI 316 stainless steel (Fig. 4). Fig. 3 — Schematic of the stress ellipsoid, which illustrates the basis of the sin 2 ψ technique. Fig. 4 — After 2000 on-off cycles under steam at 6.9 MPa (1000 psi) and 315°C (600°F), the full bore NPS 3 CL600 valve (coated by a 50-µm-thick W-WC layer deposited by CVD) failure was caused by a sealing surface design that induced contact pressures exceeding the capacity of the coating system. The bond line coating is plastically deformed at the interface with the stainless steel ball. JTST HIGHLIGHTS 14