Influence of Dwell Time and Pressure on SPS Process with Titanium Aluminides

Spark plasma sintering (SPS) or the field-assisted sintering technique (FAST) is commonly used to process powders that are difficult to consolidate, more efficiently than in the conventional powder metallurgy process route. During the process, holding time and applied holding pressure influence the product’s microstructure and subsequently its properties. In this study, in addition to the temperature impact, the influence of pressure and dwell time on the consolidation behaviour of titanium aluminide (TiAl) powders during the SPS process is investigated. Commercially available pre-alloyed TiAl48-2Cr-2Nb (GE48) and TiAl44-4Nb-0.7Mo-0.1B (TNM) powders were used, which have a high application potential in, for example, the aerospace industry. The results were evaluated based on microstructural analyses, hardness measurements and relative density calculations. It was shown that the investigated parameters significantly influence the sintering results, especially in the low temperature range. Depending on the temperature field in the sample, complete sintering is not achieved if the dwell time is too short in combination with too low a pressure. Above a certain temperature, the impact of holding pressure and holding time is significantly lower.

Additive Manufacturing (AM)

The need for less weight and high-performance materials in manufacturing industries has continuously led to the development of lightweight materials through the use of advanced additive manufacturing (AM). The race of lightweight and high-performance metals continue to evolve as this continuously provides better understanding about connection existing between material processing, microstructural development, and material properties. AM technique is an interesting manufacturing process that is employed in production of engineering components with improved properties. The choice of titanium and its alloys in structural applications are attributed to their superior strength-to-weight ratio and high corrosion resistance. This chapter looked at different additive manufacturing (AM) techniques developed for the processing of lightweight metals, their strengths, and limitations. The chapter also looked at the role and contribution of AM to the 4th industrial revolution, processing, and application of titanium aluminide for high temperature applications.

Application of cold gas dynamic spraying as an additive technology for producing materials based on nickel aluminide and titanium aluminide

Metal additive manufacturing is widely studied for its unique advantages over traditional manufacturing processes. It is used to form complex components of Ti, Fe or Ni alloys. However, for non-ferrous alloys – aluminum, magnesium, copper – additive technologies are not used due to rapid melting during laser, electron beam and/or arc treatment. Cold spraying is widely used as an effective technology for applying high quality coatings in the mass production of metal and alloy products and/or metal matrix composite coatings. In addition, cold spraying is a serious and effective tool for the additive manufacturing of metals, and research in this area is currently becoming intense. During heat treatment of materials obtained by cold spraying, new chemical compounds are formed – both intermetallic compounds and hardening ceramic inclusions that increase the microhardness. However, as a result of a change in the structure during chemical transformations, a change in the geometry of the product and the formation of pores can be observed.

Improved eddy current testing sensitivity using phase information

This paper describes a two-coil eddy current sensor being used in a transmit-receive arrangement at 1 MHz, where the drive and amplification electronics are miniaturised and built directly behind the coil to reduce noise and the effects from cable length. Small, simulated defects are detected, less than 500 microns in length, on titanium and titanium aluminide, which is an increasingly important alloy for aerospace applications. Data is analysed quantitatively in a parametric approach. This experiment uses a transmitting coil driven by a constant current source and a separate receiving coil, where the magnitude and phase of the induced voltage signals on both coils are measured independently. Experimental measurements are validated using finite element modelling and the phase of the signal on the receiving coil in particular is less susceptible to variations caused by changes in lift-off. A combination of experimental and simulation data of 2D surface scans and lift-off measurements show the variation in the magnitude and phase of the eddy current signal with lift-off on Ti, TiAl (Ti-45Al-2Mn-2Nb-1B) and 316L stainless steel. It is also shown that the high-frequency lower noise approach can reliably detect defects of less than 500 microns in length in both Ti and TiAl.