Laser Engineered Net Shaping (LENS) is a novel manufacturing process for fabricating metaI parts directly from Computer Aided Design (CAD) solid models. The process is similar to rapid prototyping technologies in its approach to fabricate a solid component by layer additive methods. However, the LENS technology is unique in that fully dense metal components with material properties that are similar to that of wrought materials can be fabricated. The LENS process has the potential to dramatically reduce the time and cost required realizing functional metal parts. In addition, the process can fabricate complex internal features not possible using existing manufacturing processes. The real promise of the technology is the potential to manipulate the material fabrication and properties through precision deposition of the material, which includes thermal behavior control, layered or graded deposition of multi-materials, and process parameter selection.

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a b s t r a c t Dissimilar metal bonds between CuCrZr and 316L stainless steel were prepared using two different solid state joining techniques. In the first instance, hot isostatic pressing, a high temperature diffusion bonding process was used to join the copper alloy to the stainless steel substrate at temperatures near 1000 • C. In the second instance, explosion bonding at ambient temperature was employed. These two techniques both yielded mechanically robust joints, where the strength of the interface exceeded that of the copper alloy, the weaker of the two substrates. However, the two bonding techniques produced near-joint microstructures that were very different. The microstructure and mechanical performance of CuCrZr/316L stainless steel joints prepared via both techniques are compared. Microstructural analysis of the joints included scanning electron microscopy, electron microprobe analysis and Auger spectroscopy techniques. The bulk mechanical properties of the substrate alloys were very different as well and are described. Particular emphasis is placed on the residual mechanical properties of the CuCrZr after thermal processing that simulate beryllium tile bonding since once the Be tiles are in place, the copper alloy cannot be solutionized and age-hardened to return it to full strength.

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Laser Engineered Net Shaping (LENS) is a direct fabrication process in which metal powders are deposited into a laser melted pool, with succeeding layers being deposited to build up complex engineering shapes. This process is a rapid, low cost, low footprint, direct fabrication technique that lends itself to the concept for advanced manufacturing. It is especially suited for rapid prototyping and small lot production. However, previous work has developed LENS as an advanced manufacturing tool, rather than exploiting its potentially unique attributes. These attributes include: real time control of microstructure, tailored material properties at different locations in the same part, the production of graded thermal expansion parts, etc. In this program, the important metallurgical parameters, solidification velocity and cooling rate, have been characterized and process models developed that are being used as input to microstructural models. Residual stresses were measured and process maps developed for controlling residual stresses and melt pool size that are critical for controlling part dimensions and quality. Tool steels and two stainless steels have been used as model systems to demonstrate the concept and feasibility of utilizing the high solidification velocities and cooling rates to design microstructures and properties to meet functionality. It has also been shown that starting powder characteristics can greatly affect build quality, especially intralayer porosity. Limited work on ceramic materials indicates that novel material can be fabricated using this technology. This work has added a new dimension in designing and fabricating engineering components with novel microstructures and properties using this rapid prototyping technology.3