Assignment 1Corrosion Engineering ECH5804Surgical implants are used to replace a large number of body parts. The head of the femur is the second most frequently replaced part of the body (after teeth!). Successful implants require three important features: they must be biocompatible, they must perform mechanically and they must be cost effective.Biocompatibility means that the material should not corrode in body fluid, and that human tissue should tolerate the material and its wear and degradation products. Body fluids are aqueous salt solutions and corrosion rates in seawater give a good estimate of corrosion rates in the body. Tissue tolerance in humans can be ranked by testing materials implanted into related animals and in assessing inflammation and the immune response. Mechanical properties required are strength and specific strength, stiffness, fatigue resistance (the hip of an average person will experience 2.5 million cycles per year), and wear resistance.

A number of materials have been used for this application. They include: a 316L stainless steel (Fe, 17.5%Cr, 13.5%Ni, 2.6%Mo), Co-Ni-Cr-Mo (MP35N) alloy (Co, 20%Cr, 35%Ni, 9.5%Mo), a Titanium alloy (Ti, 6%Al, 4.3%V) and Tantalum (Ta) metal which is very corrosion resistant. The properties of these materials are listed in the Table below.

Which material would you select for this application? Justify your selection quantitatively taking into account the relative importance of the different properties

Property316LMP35NTi-6Al-4VTa

Yield Strength (MPa)689879830345

Density89417

Hardness88998375

Stress Amplitude (MPa) for 107 cycles570600490300

Modulus (GPa)200242124190190

Corrosion in seawater (um/year)2.5101

Tissue tolerance ranking (higher the better91078

Cost (relative)13375