The present disclosure relates generally to methods for treating surfaces of metal items. In particular, methods of treating surfaces of cast zirconium alloy based medical implants are described.
Known methods of producing zirconium alloy based medical implants are not entirely satisfactory for the range of applications in which they are employed. Zirconium alloys, and Zirconium-2.5 Niobium in particular, has been used to in medical implants for weight bearing components, such as femoral heads and knee replacement femoral components. One benefit of using zirconium alloy is that an oxidation process can be readily applied to create a substantially dense, smooth, and uniform layer of zirconium oxide, which defines a low friction coefficient and is exceptionally hard.
An oxidation layer provides numerous operational benefits, such as superior resistance to wear and corrosion. These specific benefits are particularly relevant in the medical implant industry because malfunctioning implants could cause bodily injury or require invasive implants surgery to repair. The low friction coefficient of oxide layers tend to reduce wear when the oxide surfaces articulates against relatively soft materials, such as plastic implants paired with metal implants
Both cast and forged zirconium alloy based medical implants can meet relevant American Society for Testing and Materials International (“ASTM”) chemical and mechanical requirements for medical implants. Cast alloy parts, however, are significantly cheaper to manufacture than forged analogues. Cast alloy parts, prior to many of the innovations described in this disclosure, have historically produced lower quality products, however.
For example, many cast zirconium alloy parts have had unsatisfactory surface conditions to enable zirconium oxide layers to a desired extent. For example, many cast zirconium alloy products define large, visible grain boundaries, which often result in uneven and cracked zirconium oxide layers when the products are oxidized. Further, these imperfections often result in a product that visually appears unreliable, which may lower medical practitioners' confidence in them.
Each of these limitations of conventional zirconium alloy casting processes result in lower quality products. The lower quality products typically have less dense, smooth, and form surfaces and lack the resistance to corrosion and wear of forged products. As a result, conventional cast zirconium alloy parts are not cost-effective, suitable replacements for forged zirconium alloy parts.
Thus, there exists a need for processes for producing cast zirconium alloy products that that improve upon and advance the design of known methods. In particular, the field requires methods to increase the quality of the zirconium oxide layer of cast zirconium alloy products. Even more particularly, there exists a need for methods of preparing the surface of cast zirconium alloy products with improved surface characteristics prior to creating the oxidized layer.
It would be desirable to increase the quality of the oxidized layer of cast products to produce a cost-effective and suitable replacement of forged zirconium alloy products. Indeed, it would be desirable to produce high-quality zirconium alloy products at a significantly lower price than conventional forged products. Examples of new and useful methods relevant to increasing cast products' quality are described below.