Abstract
Microstructural deformation mechanisms present during three different forming processes in commercially pure Ti were analysed. Room temperature mechanical forming, laser beam forming and a combination of these two processes were applied to thick metal plates in order to achieve the same final shape. An electron backscatter diffraction technique was used to study the plate microstructure before and after applying the forming processes. Substantial differences among the main deformation mechanisms were clearly detected. In pure mechanical forming at room temperature, mechanical twinning predominates in both compression and tensile areas. A dislocation slip mechanism inside the compression and tensile area is characteristic of the pure laser forming process. Forming processes which subsequently combine the laser and mechanical approaches result in a combination of twinning and dislocation mechanisms. The Schmid factor at an individual grain level, the local temperature and the strain rate are factors that determine which deformation mechanism will prevail at the microscopic level. The final microstructures obtained after the different forming processes were applied are discussed from the point of view of their influence on the performance of the resulting formed product. The observations suggest that phase transformation in Ti is an additional microstructural factor that has to be considered during laser forming.
Highlights
The high specific strength and excellent corrosion resistance are what makes titanium-based alloys attractive material for use in the aerospace industry
The laser forming and partial of the laser–mechanical forming show a very fine hexagonal martensitic phase (a0), i.e. acicular martensite which is a typical effect for quenched pure titanium [15]
A general observation is that laser forming utilizes plastic deformation at high temperatures, while mechanical forming at room temperature is characterized by plastic deformation at low temperature
Summary
The high specific strength and excellent corrosion resistance are what makes titanium-based alloys attractive material for use in the aerospace industry. Ti exhibits a high melting temperature and can be used at high temperatures (around 800 K) with excellent toughness and creep properties. Despite the numerous advantages such as the highest specific strength (yield strength-to-weight ratio) of any metal, it exhibits poor tribological and less advanced fatigue properties. In the domain of manufacturing, mechanical forming (MF) is a frequently used industrial process on titanium. Laser forming of a sheet metal in two-dimensional shapes was first reported by Namba [1] in 1985. Laser forming has been applied to industrial processes in the naval construction industry using flat steel plates which have to be formed into three-dimensional shapes [2,3,4,5]. A number of the latest developments, techniques and modelling procedures for laser forming have been reviewed in [8]
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