Investigation of metallic structure with negative thermal expansion: A review

Materials with negative thermal expansion (NTE) properties have numerous applications that interest design engineers and scientists in aerospace, electronics, dentistry and other industries and fields that at some stage experience unwanted thermal expansion in parts. This paper reviews research done on developing metal alloys or solid structures from combination of metal alloys that demonstrate negative thermal expansion properties. The review shows that a variety of alloys, composites and structures have been used to develop NTE metallic structures some of which have achieved significant successes in doing so. In order to fabricate parts from a mix of alloys or a structure comprising a series of layers from various alloys, a technology with high flexibility was needed. Traditional welding or casting methods could not offer such capabilities. Direct Metal Deposition (DMD) is a technology that uses laser energy to melt metal powder injected coaxially with the laser beam on substrates and create shapes and structures directly from CAD models with none or minimal metallurgical defects. The technology will be used to explore the manufacture of complex structures with NTE properties using a range of alloying powders.