Relating porosity and mechanical properties in spray formed tubulars

Because the spray forming process holds the potential to reduce the cost of alloy production, there is significant interest in developing methods to industrialized and automate this process through advanced sensing techniques. These advanced sensing techniques will observe the process real-time and give inputs to a process controller. By determining relationships between part quality, process parameters and sensor inputs, the process controller will be able to determine the quality of a part while it is being made and make adjustments if necessary. A Tinius-Olsen Tensile Tester was used to test five tensile specimens. The five tensile specimens were taken from five alloy 625 (60% Ni, 20% Cr, 8%Mo, 5% Fe) tubulars with varying properties. Among the advanced sensing techniques currently used to monitor the spray forming process is a surface roughness sensor. It consists of an argon laser, a charge coupled device (CCD) camera and roughness determination software. The laser emission is expanded into a long, thin line and projected onto the substrate as the molten metal consolidates on the surface. The roughness determination software will grab a frame with the laser stripe, digitize it and calculate the root mean square (RMS) value of the roughness in that particular frame. Each frame has a time stamp and can be related back to other time stamped process parameters. Recent sensor work has tried to find correlations between RMS values and porosities determined after processing. This venture has met with limited success. The object of this paper is to link porosity with mechanical properties and therefore define quality. Eventually the input from all sensors and process parameters will be entered into a process controller. If there is a link between sensor data and quality, this controller will be able to determine the quality of a forming material from sensor inputs and make changes in the process parameters if the quality is poor