This study investigates the development of fatigue failure in steel specimens coated by various spraying methods with and without grit blasting. Commercial titanium powder was deposited on structural steel substrates by low-pressure and portable cold spray as well as plasma and warm spray. Coating samples were subjected to strain-controlled cyclic bending, while monitoring resonant frequency as a measure of accumulated damage. A change in frequency of 4 Hz was chosen as the test-stop with the corresponding cycle count serving as the main indicator of fatigue life. Test results are presented in the paper along with explanations of fatigue mechanisms and process-related factors.

Superior characteristics of the cold sprayed coating have led to many high-tech applications. Until recently, all these applications were carried out using ‘stationary’ systems only, while some applications such as in-situ repair of aircraft body/engine parts require a portable system. Recently a ‘Portable High Pressure Cold Spray System’ called KINETIKS 2000-2 has been developed. This system is capable of 400 C/20 bars nitrogen/helium jet, and produces dense coatings with clean interfaces of many materials. In order to establish the suitability of this process for producing aluminum alloy coatings for aerospace and other high tech industries, various aluminum alloys (CP-Al, HP-Al, 6061 Al, 7005 Al) coatings were produced over many substrate materials (2024 Al, 7005 Al, 4041 Steel, ZE41A Mg). Coatings were characterized using microstructure, bond strength, bend test, corrosion studies, etc. Microstructural study showed that dense coatings with about 2-4% porosity values were produced with clean and well bonded interfaces. Bond strength of these coatings varied between 20 to 35 MPa, Bend test results showed that the coatings have adequate strengths and could withstand severe strain conditions. Salt fog corrosion studies (ASTM B 117) showed that the coatings impart corrosion resistance to the substrates.

Cold spray produces superior coatings with many unique properties, which have led to many new applications of sprayed coatings. In a few applications, such as in-situ repair of aircraft body/engine parts, etc., a portable system is required. Though some portable low pressure (5 – 10 bars) systems are available, these systems have many limitations on coating materials and coating qualities. Recently a ‘Portable high pressure cold spray system’, called Kinetiks 2000, has been developed. Kinetiks 2000 system can operate at 400 °C max nitrogen temperature and 20 bars max gas pressure. A touch panel on the console is used to input and control the process parameters. A hand held gun with a filament heater and a gun body, mounted directly onto the heater, is used for manual spray. This system operates with two different powder hoppers. Coatings of many materials, including aluminum, copper, titanium, zinc, etc have been produced. Microstructural investigations of sprayed coatings have shown that good, strong, dense coatings with clean interfaces and strong bonding to various substrates can be produced. Experiments are continuing to quantify the process characteristics and record the properties of sprayed coatings.