Optimization of Atmospheric Plasma Spray Process Parameters using a Design of Experiment for Alloy 625 coatings

Abstract

Alloy 625 is a Ni-based superalloy which is often a good solution to surface engineering problems involving high temperature corrosion, wear, and thermal degradation. Coatings of alloy 625 can be efficiently deposited by thermal spray methods such as Air Plasma Spraying. As in all thermal spray processes, the final properties of the coatings are determined by the spraying parameters. In the present study, a D-optimal experimental design was used to characterize the effects of the APS process parameters on in-flight particle temperature and velocity, and on the oxide content and porosity in the coatings. These results were used to create an empirical model to predict the optimum deposition conditions. A second set of coatings was then deposited to test the model predictions. The optimum spraying conditions produced a coating with less than 4% oxide and less than 2.5% porosity. The process parameters which exhibited the most important effects directly on the oxide content in the coating were particle size, spray distance, and Ar flow rate. The parameters with the largest effects directly on porosity were spray distance, particle size, and current. The particle size, current, and Ar flow rate have an influence on particle velocity and temperature but spray distance did not have a significant effect on either of those characteristics. Thus, knowledge of the in-flight particle characteristics alone was not sufficient to control the final microstructure. The oxidation index and the melting index incorporate all the parameters that were found to be significant in the statistical analyses and correlate well with the measured oxide content and porosity in the coatings.

Plasma Sprayed Bioceramic Coatings on Ti-Based Substrates: Methods for Investigation of Their Crystallographic Structures and Mechanical Properties

“…Due to the complexity of the plasma-spraying process, the technological conditions play a crucial role and can significantly influence the coating structure and practical performance (Azarmi et al, 2008;Frayssinet et al, 2006;Sampath et al, 2003).…”

“…The technological regime during plasma-spraying is mainly defined by the following parameters (Azarmi et al, 2008;Harsha et al, 2008;Sarikaya, 2005;Skulev et al, 2005):…”

“…This in turn has brought the necessity of more precise evaluation and control of the micro-structure parameters and technological conditions during plasmaspraying. As a result, further improvement of the existing and development of new experimental and theoretical methods and models for prognosis, investigation and control of the structure formation processes, technological parameters and operational properties has been provoked (Azarmi et al, 2008;Chen et al, 1993;Fan et al, 2005;Iordanova & Forcey, 1997;Kuroda & Clyne, 1991;Liu et al, 2005;Mawdsley et al, 2001;Moreau et al, 2005;Parizi et al, 2007;Sampath et al, 2003;Sarikaya, 2005;Toma et al, 2003). The main aim of this general trend for research and investigation, observed at present, is optimisation of the plasma-spraying technology to achieve superior parameters of the deposited bioceramic coatings enabling their successful and reliable long-term utilisation in a wide range of biomedical applications.…”

“…New methods for non-destructive control, including statistical evaluation of the collected data, together with prognosis of the coating parameters as a function of the technological conditions have been offered as well (Zhu & Ding, 2000). Some work has already been done to characterise the following main dependencies that play an important role for successful performance of the discussed biomedical coatings (Azarmi et al, 2008;Boulos et al, 1993;Celik et al, 1999;Chen et al, 1993;Choi et al, 1998;Dyshlovenko et al, 2005;Fan et al, 2005;Gueorguiev et al, 2008aGueorguiev et al, , 2008cIordanova & Forcey, 1997;Khor et al, 2004;Kreye et al, 2007;Kuroda & Clyne, 1991;Leigh & Berndt, 1997;Li & Khor, 2002;Liu et al, 2005;Lugscheiber et al, 1993;Mawdsley et al, 2001;Montavon et al, 1997;Moreau et al, 2005;Neufuss et al, 2001;Ohmori & Li, 1991;Parizi et al, 2007;Sampath et al, 2003;Sarikaya, 2005;Srinivasan et al, 2006;Staia et al, 2001;Streibl et al, 2006;Toma et al, 2003;Tong et al, 1996;Wallace & Ilavsky, 1998;Zhu & Ding, 2000):…”

Microstructure Characterization of Alloy 625 Deposited on Nickel Foam using Air Plasma Spraying

“…Therefore, the microstructural characteristics of the coating which affect its mechanical properties are more critical than in conventional applications of thermal spray deposits, and require thorough investigation. Porosity is known to decrease the elastic moduli and strength of thermal plasma coatings, [14] and the presence of oxide phases can be expected to reduce the ductility substantially.In a previous study of the APS deposition of alloy 625 coatings, [15,16] spray parameters optimized to produce homogenous coatings with minimum porosity and oxide content on stainless steel substrates were identified. In anticipation of the production of foam core sandwich structures, the present paper examines in more detail the microstructure and phase composition of alloy 625 coatings deposited by APS on coupons of graphite filled nickel foam (Fig.…”