Structure and Properties of Co-Cr-Mo Alloy Manufactured by Powder Injection Molding Method

Abstract

Cobalt–chromium–molybdenum alloys samples were obtained by the powder injection molding method (PIM). PIM is dedicated to the mass production of components and can manufacture several grades of dental screws, bolts, stabilizers, or implants. As a skeleton component, ethylene–vinyl acetate (EVA copolymer) with a low temperature of processing and softening point was used. The choice of a low-temperature binder made it necessary to use a coarse ceramic powder as a mechanical support of the green sample during sintering. The injection-molded materials were thermally degraded in N2 or Ar-5%H2 and further sintered in N2-5%H2 or Ar-5%H2 at 1300 or 1350 °C for 30 min. The structure of the obtained samples was characterized by X-ray diffraction and electron microscopy. Mechanical properties, including hardness and three-point bending tests, confirmed that a nitrogen-rich atmosphere significantly increases the bending strength compared to the material manufactured in Ar-5%H2. This is due to the precipitation of numerous fine nitrides and intermetallic phases that strengthen the ductile γ-phase matrix.

A review on manufacturing processes of cobalt‐chromium alloy implants and its impact on corrosion resistance and biocompatibility

“…Powder metallurgy is a manufacturing process where metal powders are pressed into a rigid die under intense pressure followed by heat treating (sintering) of the compacted powder to impart strength and integrity 98 . During powder metallurgy, parameters such as powder properties (shape, size, and powder‐to‐binder ratios), compaction pressure, sintering temperature, sintering time, sintering atmosphere, and cooling rate must be carefully controlled as these parameters affect the structure and properties of the formed component 107–109 . In addition, the type of gas used during sintering must be carefully selected to protect the alloy from oxidation and contamination 110 .…”

“…[107][108][109] In addition, the type of gas used during sintering must be carefully selected to protect the alloy from oxidation and contamination. 110 The advantages 107,111 of the powder metallurgy process includes (a) complex shapes can be obtained that closely imitates the geometry of anatomical structures;…”

“…98 During powder metallurgy, parameters such as powder properties (shape, size, and powder-to-binder ratios), compaction pressure, sintering temperature, sintering time, sintering atmosphere, and cooling rate must be carefully controlled as these parameters affect the structure and properties of the formed component. [107][108][109] In addition, the type of gas used during sintering must be carefully selected to protect the alloy from oxidation and contamination. 110 The advantages 107,111 of the powder metallurgy process includes (a) complex shapes can be obtained that closely imitates the geometry of anatomical structures;…”

“…The component is then sintered to achieve the desired mechanical properties. Matula et al 107 used CoCrMo alloy powder (64%), paraffin wax (16%), stearic acid (4%) and ethylene-vinyl acetate (16%) binder to produce PIM samples.…”

“…In addition, the type of gas used during sintering must be carefully selected to protect the alloy from oxidation and contamination 110 . The advantages 107,111 of the powder metallurgy process includes (a) complex shapes can be obtained that closely imitates the geometry of anatomical structures; (b) multi‐layered structures can be obtained with desired physical, chemical, and mechanical properties; (c) the porosity of the material can be regulated to promote osseointegration; and (d) when compared to cast and wrought alloys, the components made by powder metallurgy have higher tensile and fatigue strength, increased hardness, finer grain size, and more uniform microstructure 111 . The methods that are used to prepare CoCr alloys such as hot isostatic pressing (HIP) and metal injection molding (MIM) are based on the powder metallurgy process.…”