This Small Business Innovation Research (SBIR) Phase I project aims to develop a hybrid magnetron sputtering deposition process to apply alloy coatings on substrates as the replacement of electrolytic hard chrome (EHC) plating that utilizes hexavalent solution, a known carcinogen. Conventional magnetron sputtering is superior to other potential EHC replacement processes, such as electroless plating and high velocity oxygen fuel spray (HVOF) in terms of environmental impact, post machining, process temperature, adhesion to substrates, uniformity, and metallic luster. In this project, a hybrid process will be used to overcome the drawbacks of low deposition rate, limited ionization, low target utilization, and strictly line of sight deposition of traditional magnetron sputtering. Chromium coatings will be deposited in a batch coater using customized deposition hardware. It is anticipated that the resulted coatings can be applied not only to new parts for wear and corrosion protection, but also to worn parts for repair.
The broader/commercial impact of this project will be the potential to replace EHC plating with an environmentally-benign, high deposition rate, and relatively low-cost hybrid magnetron sputtering process. The replacement will answer the urgent calls from federal agencies and international bodies to phase out EHC, eliminate carcinogenic mist exposure to plating shop operators, and provide current manufacturers an easy process for their critical hard coating needs. The expected outcomes of this project are process know-how and a proprietary coating system.
Electrolytic hard chrome (EHC) coatings are used in numerous applications for protection of components and structures against wear and corrosion. EHC plating utilizes hexavalent solution, which is carcinogenic and restricted increasingly by regulations. So far, electroless nickel plating and high velocity oxygen fuel (HVOF) spray have emerged as the major replacement processes for EHC plating. However, both have suffered major limitations to become viable replacement of EHC. Electroless Ni plating is a wet bath process and subject to tight environment regulations itself. It is limited to thin coatings and needs post heat treatment for desired hardness. HVOF is a high temperature deposition and line of sight process mainly for ceramic and refractive coatings, which can hardly be applied to temperature sensible substrates. The process control and post-machining are difficult. Although hard enough, ceramic and refractive coatings by HVOF are no equivalent to EHC coatings for their color luster, metallurgical bond to substrate, proven compatibility with mating surfaces, and suitability for conformal and deep bore components. To that end, Ultool proposed deposition of hard chrome or alloy coatings to replace EHC by employing a hybrid magnetron sputtering process. Ultool expected that the proposed hybrid magnetron sputtering process would outperform electroless Ni plating and HVOF spray in terms of more benign process, easier process control, less post-deposition machining, and better coating quality. In this SBIR Phase I project, Ultool has designed, prototyped, and demonstrated a firs-of-a-kind hybrid magnetron sputtering source that shows the following advantages: 1) Easy ignition. 2) Stable Plasma. 3) Low deposition voltage and high deposition current. 4) Good coating quality. 5) DC Reactive magnetron sputtering. 6) Easy adoption in conventional sputtering coaters. 7) Potential for deep bore coatings. Using the developed hybrid sputtering source, Ultool has deposited Cr and CrN coatings on stainless steel substrates and silicon wafers. The feasibility is proven by the following findings: 1) The hybrid magnetron sputtering source developed is a viable deposition tool that can be installed in a conventional sputtering coater and driven by an off-the-shelf DC power supply. 2) Operation parameters (chamber pressure, partial pressure of process gases, and power) of the hybrid magnetron sputtering process can be easily and independently controlled. 3) Cr coatings can be deposited on 304 stainless steel substrates using the hybrid magnetron sputtering source. 4) CrN coatings can be deposited using DC power supply without any sign of arcing and target poisoning. 5) The hybrid magnetron sputtering process can operate continuously for hours, which indicates sufficient cathode/anode cooling. The broader/commercial impact of this project will be the replacement of EHC plating by an environmentally-benign, high deposition rate, and relatively low-cost hybrid magnetron sputtering process. The replacement will answer the urgent calls from federal agencies and international bodies to phase out EHC, eliminate carcinogenic mist exposure of plating shop operators, and provide current manufacturers an easy process for their critical hard coating needs. The expected outcomes of this research are process know-how and a proprietary coating system.
