Effects of printing parameters on density and mechanical properties of binder jet printed WC-Co Pierangeli Rodríguez De Vecchisa, Danielle Brunettaa, Katerina Kimesa, Drew Elhassida and Markus Chmielusa Department of Mechanical Engineering and Materials Science, University of Pittsburgh a
Pierangeli Rodríguez De Vecchis
Dr. Markus Chmielus
Pierangeli Rodríguez De Vecchis is a Materials Science and Engineering senior. She works in Dr. Chmielus lab on Binder Jet 3D Printing (BJ3DP). She has been awarded the sophomore and junior PCEASASM and WAAIME scholarships. She is the vice-president of materials advantage 2019-2020. Dr. Markus Chmielus is an Associate professor at the University of Pittsburgh (MEMS). His research is focused on binder jet printing of metal alloys and the study of magneto-caloric materials. He teaches Junior and Senior Materials Science classes and is the Advisor for the Material Advantage Chapter.
Significance Statement
Traditional manufacturing of WC-Co parts is slow and expensive, while Additive Manufacturing offers a commercially viable and fast solution. This project shows how choosing optimal printing parameters for binder jet printing (BJP) can produce parts with equally excellent mechanical properties, allowing to pair WC-Co (complex material) with BJP (innovative technology).
Category: Methods
Keywords: Binder jet printing, tungsten carbide, printing parameter, design of experiments.
88 Undergraduate Research at the Swanson School of Engineering
Abstract
Tungsten carbide-cobalt (WC-Co) is a cermet material widely known for its excellent combination of mechanical properties including high hardness provided by small WC grains, and high toughness provided by the Co-matrix binder metal. Its applications range from mining and drilling tools to cutting gears. Traditionally, WC-Co parts are formed through powder metallurgy processes. The WC and Co mixed powders are typically pressed with added wax that results in a low-density part, which is later put through a de-waxing and hot isostatic pressing (HIP) process. However, this process demands mass production resulting in a slow and expensive process. Additive Manufacturing, particularly binder jet-printing (BJP) appeared as an option to supplement traditional WC-Co manufacturing, allowing the production of fast, specific, and highly detailed parts. A design of experiments was set-up to find the optimal printing parameters to form parts with high green densities, translating to high hardness and fracture toughness. The highest green densities were obtained with a 220% binder saturation, 45 s drying time, 100 µm layer thickness, 5 mm/sec roller speed, and a build-to-feed ratio of 2. Sintered-HIPed parts resulted in 99% relative density, 1310 HV hardness and 14.74 MPam0.5 fracture toughness.
1. Introduction
Tungsten carbide-cobalt (WC-Co), also known as cemented carbide is a cermet (ceramic-metal) material widely known for its excellent mechanical properties (including high density, hardness, toughness and flexural stress). It is used in wear resistant applications, including machining, cutting, and rolling, as well as mining and oil drilling tools [1]. Morphologically, the WC-Co microstructure is composed of hard/brittle, small, polygonal WC grains within a tough Co matrix. Co is known as the binder metal as it is chosen to melt at a lower temperature than WC to wet the grains and allow strong metallic bonds to form between WC particles during sintering, reducing brittleness without greatly decreasing hardness [2]. Traditionally, WC-Co parts are manufactured by powder metallurgy through which WC and Co particles are blended and ball-milled, after having previously carbonized W, typically with carbon monoxide (CO). Parts are formed through mechanical pressing or molding to obtain a green state. A small amount of paraffin is added to increase its density which is removed through a de-waxing process, followed by sintering and hot isostatic pressing (HIP), resulting in the final, fully dense cermet part [3]. This technology is slow and expensive, requiring the mass production of molds and limited in resolution. As a result, additive manufacturing (AM) appeared as an option to create WC-Co shapes fast and with specific design requirements. The focus of this project is the AM technology of binder-jet printing (BJP). BJP has the potential to produce WC-Co objects by selectively stacking layers of powder and binder alternatively, according to a computer design, as shown in Figure 1. It is a fast, cost-effective process that allows the formation of complex internal and external geometries [4]. In contrast with other AM
