Aspects related to the metal composition

1 Importance of materials purity in improving the corrosion resistance 

The evolution of stainless steel composition can be used to illustrate the importance of materials purity in reducing corrosion susceptibility. Chromium and molybdenum are the key elements in promoting resistance to pitting and crevice attack of stainless steels, but high chromium and molybdenum concentrations are not sufficient to ensure an adequate corrosion resistance. Low concentrations of impurities, like carbon, silicon, phosphorous and sulphur, are required. Type 316L and 316LVM stainless steels are commonly employed to fabricate a variety of fracture fixation devices. They both have low carbon concentration, below 0.03 wt%, which is indicated by the letter L. VM stands for vacuum-melted, a technique 

Due to the presence of a thin oxide film, titanium has a very high corrosion resistance. However, its low resistance under wear conditions may lead to enormously high titanium concentrations in tissues adjacent to titanium implants (section 9.3.1). Rapid film formation after surface damage is therefore of critical importance to guarantee low levels of titanium ions. 

A new alloy, Ti-15Zr-4Nb-2Ta-0.2Pd, with better corrosion resistance than the conventional Ti-6A1-4V, was proposed by the same authors. 

Although not as widely used as titanium, tantalum has found a number of applications, e.g. in vascular clips, as a suture and to fabricate flexible stents to prevent arterial collapse. The reader is referred to a paper by J. Black (1994), where the material properties are reviewed, together with 

---