Development of Cutting Tool Through Superplastic Boronizing of Duplex Stainless Steel
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INTRODUCTION
TODAY’S ever-growing demand in machining process calls for the production of high-performance cutting tools, which require many improvements in regard to the substrates, processes, and coating involved. The most established substrates or tool materials are comprised of high-speed steels (HSSs), sintered carbide or cemented carbide, ceramic, and extra-hard materials. Most of these tool materials are processed at high pressure and high temperature in order to produce them. For example, ceramic materials are molded from ceramic powder at a pressure of more than 25 MPa, to be sintered later at approximately 1973 K (1700 °C).[1] This shows that the process involves the use of high energy, which implies high cost. Coating, an enhancement feature in most tool substrates, is done to improve their resistance to wear and tear such as oxidation, metal fatigue, thermal shock, and reducing frictions. Among the common coating methods employed are chemical vapor deposition (CVD) and physical vapor deposition (PVD). The CVD of films and coatings involves the chemical reactions of gaseous reactants on or near the vicinity of a heated substrate surface.[2–4] However, some difficulties have been found in the process, causing it to result in complicated chemical systems. The PVD process involves solid or liquid source evaporated into the gas phase, which is in turn deposited into the solid phase. One drawback found is this process’s line of sight, which makes even coating for complicated geometries challenging.[3–5] From an industrial point of
ISWADI JAUHARI, SUNITA HARUN, SITI AIDA JAMLUS, and MOHD FAIZUL MOHD SABRI are with the Department of Mechanical Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia. Contact e-mail: [email protected] Manuscript submitted May 5, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
view, this shows that the methods are quite complicated with high capital cost, and apart from that, only simple geometries can be coated evenly. Boronizing is a thermochemical surface treatment process involving atom diffusion in the surface of the substrate material to form a boride layer. The process is used to strengthen resistance to corrosion and abrasive wear, decrease the coefficient of friction (COF), and, of course, greatly increase surface hardness. Recent developments in boronizing have shown that it can be applied to the WC cutting tool to enhance titanium alloy machining.[6] However, a high processing cost is expected in this method. Superplasticity is known as a phenomenon of solid material that exhibits large deformation at high temperature. Superplastic boronizing is a process of conducting boronizing while the specimen is concurrently superplastically deformed. Superplastic boronizing is quite similar to hot isostatic pressing; it is performed at an elevated temperature with pressure applied from all directions. Prior studies have been conducted on superplastic boronizing of duplex stainless steel (DSS) under initial pressure conditions.[7] Good results are obtained from the aspect of t
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