Spark Plasma Sintering of Graded Dissimilar Metals

An attempt was made to produce graded stainless steel (SS)/commercially pure titanium (Ti) samples using spark plasma sintering. A cylindrical sample of 20 mm diameter and 38 mm height, consisting of six layers with decreasing amounts of Ti (in steps of similar to 20 vol.%) from layer L-1 (100 vol.% Ti) to layer L-6 (100 vol.% SS), was targeted. After process optimization, fully dense, graded SS/Ti samples were successfully produced. However, the samples showed several different intermetallics such as FeTi, NiTi, Fe2Ti, and Cr2Ti. The intermetallic formation was found to be most severe in layer L-5 (80 vol.% SS + 20 vol.% Ti). These graded SS/Ti samples exhibited a tensile strength of 280 +/- 9 MPa and were found to suffer brittle fractures in layer L-5. In subsequent experiments, attempts were made to overcome this problem using temperature gradient sintering and/or ball-milled SS powder. While the combined use of temperature gradient sintering and ball-milled SS powder was helpful in improving the tensile strength of graded SS/Ti samples to 320 +/- 12 MPa, undesirable intermetallic formation and brittle fractures in layer L-5 could not be avoided.