Plasma residual stresses

In the case of a photoresist, the ultimate definable feature size together with the ability of the material to withstand either chemical etchants or plasma environments determines the domain of utility. The feature size is in turn determined by the wavelength required for exposure, the sensitivity and contrast of the resist, and the dimensional stability of the material during exposure, development, and subsequent processing. Adhesion of the resist to the substrate is critical both for patterning and use, and adhesion can be affected by surface preparations, and by residual stresses developed during deposition and cure. While photo-imagable polyimides have been introduced, their principal intended application is as a component of the finished part, either as passivant or interlevel dielectric (see below). 

Residual stresses induced by variable polarity plasma arc (VPPA) welding in an A1 alloy 2219-T851 plate (6.5 mm thickness - Z direction, 62 mm in the direction parallel to the weld axis - Y direction, 48 mm in the direction perpendicular to it - X direction) were investigated by neutron diffraction [5], Measurements were performed by neutron diffraction, using the time of flight (TOF) technique, with a 2x10x2 mm3 sampling volume. 

Some examples of applications of neutron and synchrotron radiation diffraction applied to the determination of residual stresses in various industrial and technological components have been presented. The reliability of the technique has been shown, being able to determine residual stresses induced by various thermomechanical treatments, such as shrink-fit joints, welds and surface treatments in automotive and aerospace materials. It has been shown how, by this method, it is possible to determine stresses both in the coating and in the substrate of plasma-spray deposed hydroxyapatite layers on Ti alloy for biomedical applications. 

Tsui, Y.C., Doyle, C., and Clyne, T.W. (1998a) Plasma sprayed hydroxyapatite coatings on titanium substrates. Part 1 mechanical properties and residual stress levels. Biomaterials, 19, 2015-2029. 

During plasma spraying, the particle-substrate interactions characterised by momentum and heat transfer from the solidifying particle after impacting the surface of the substrate lead eventually to the development of residual stresses in the coating. These stresses can be divided into microscopic, mesoscopic and macroscopic stresses. 

Residual Stresses in Plasma-Sprayed Hydroxyapatite Coatings 7.6.6.1 Stress Analysis by X-ray Diffraction... 

Figure 7.49 Relation between adhesive failure and compressive residual stresses of plasma-sprayed hydroxyapatite coatings on Ti6AI4V. (Adapted from Yang and Chang (2001).)...

The effect of residual stress on the dissolution of hydroxyapatite coatings was investigated on plasma-sprayed coatings of 80, 110 and 200 pm thickness (Han, Xu and Lu, 2001). Residual stresses in the coatings were measured with a holedrilling method. Dissolution of the coatings was monitored along with an examination of the phase composition. The results showed that both tensile residual... 

Godoy, C., Souza, E.A., Lima, M.M., and Batista, J.C.A. (2002) Correlation between residual stresses and adhesion of plasma sprayed coatings effects of a postannealing treatment. Thin Solid Films, 420/421, 438 -445. 

Y. (2014) Effect of dissolution/precipitation on the residual stress redistribution of plasma-sprayed hydroxyapatite coatings on titanium substrate in simulated body fluid (SBF). J. Mech. Behav. Biomed. Mater. 36, 98-108. 

Noutomi, A. and Kodama, M. (1989) Residual stress measurement on plasma sprayed coatings. Weld. Int., 11, 947 —953. 

Sergo, V., Sbaizero, O., and Clarke, D.R. (1997) Mechanical and chemical consequences of the residual stresses in plasma sprayed hydroxyapatite coatings. Biomaterials, 18 (6), 477-482. 

Takeuchi, S., Ito, M., and Takeda, K. (1990) Modelling of residual stress in plasma-sprayed coatings effect of substrate temperature. Surf. Coat. Technol., 43/44 (1), 426-435. 

Yang, Y.C. (2007) Influence of residual stress on bonding strength of the plasma-sprayed hydroxyapatite coating after the vacuum heat treatment. Surf. Coat. Int., 201, 7187-7193. 

Yang, Y.C. and Chang, E. (2001) Influence of residual stress on bonding strength and fracture of plasma-sprayed hydroxyapatite coatings on Ti-6A1-4V substrate. Biomaterials, 22 (13), 1827—1836. 

It can be assumed that coatings formed from lower crystallinity particles exhibit low residual stress because feedstock also has inherent porosity that would tend to relieve process-induced stresses. A comparison of the high velocity oxy-fuel and plasma spray processes has revealed that the residual stress is lower in the former process (Knowles et al. 1996). Heat treatment at temperatures of 800°C can minimize these process-induced stresses (Brown et al. 1994). Despite the large influence of thickness on coating strength, no difference in bone apposition has been found for 50 pm and 100 pm coatings. 

Khan MA, Haque MS, Nasseem HA, Brown WD, Malshe AP (1998) Microwave plasma chemical vapor deposition of diamond films with low residual stress on large area porous siUcon substrates. Thin Solid Films 332 93-97... 

---