Microchemistry and Microhardness as a Function of Microstructure in Parallel Gap Welds 670222
A study was made on the metallographic, microchemical and microhardness properties of parallel gap welds and their relationship to each other.
The parallel gap welding process is often used to join metals with large differences in their physical properties over wide ranges of energy inputs. The resultant weld microstructures vary over a full spectrum from the so-called brazed joint to a completely fused weld area. It was the purpose of this study to determine the chemical and mechanical variations on a microscale in the weld area to aid in an intelligent interpretation of the microstructure.
The bulk of the work was done on gold plated Kovar leads (0.015 × 0.004) welded to nickel ribbon. The main conclusions may be summarized as follows:
In the braze type joint the gold plating melts and dissolves metal from the Kovar leads and the nickel ribbon. In the brazed area there are concentration gradients of the elements present in the weld members across the braze. The brazed area is two or three times the original plating thickness.
As the energy input is increased the thickness of the brazed area increases and the concentration gradient becomes less sharp.
At the highest energy inputs the entire area has melted and there is a chemically homogeneous alloy across the entire area.
Microhardness readings show evidence of solid solution harding due to alloying during the braze/welding processes.
The microchemical and microhardness studies along with the metallographic examination show that good joints are obtained in the weld joint or brazed joint and points in between.