The defect-free processing of TiAl alloy TNM™-B1 by means of Laser Powder Bed Fusion (LPBF) is demonstrated by manufacturing of an automobile turbocharger wheel. Similar precision cast material was used as reference. TNM™-B1 was manufactured crack free with a density > 99.5% using elevated process temperatures above the brittle-to-ductile transient temperature (BDTT). The preheating temperature was provided by an induction preheating system. To minimize oxygen pick up during the LPBF process, the process atmosphere was actively cleaned using a gas-purification system.

Produced test samples were analyzed in as-built and heat-treated condition regarding density, micro structure and phases by means of a Light Optical Microscope (LOM) and Scanning Electron Microscopy (SEM). Micro hardness was measured according to Vickers. Oxidation measurements were performed by means of carrier-gas hot extraction. Mechanical properties were determined using room temperature tensile tests. The final automobile turbocharger wheel was analyzed for defects using a Micro-Computer Tomography scanner (MCT).

Besides bulk test samples, thin-walled specimens can be manufactured with sufficient density. Depending on the process parameters, an oxygen content < 1000 ppm could be reached. The as-built microstructure consists of lamellar (α2+γ) colonies and nearly globular γ as well as β/β0 at the grain boundaries. High cooling rates in the magnitude of 105 to 106 K/s provide small grain sizes of 1–7 μm. Hardness measurements reveal an increased hardness (515-560HV0.3) compared to cast material (390HV0.3). Samples for tensile tests show tensile strength around 840 MPa and a total elongation of 1.1% for LPBF-manufactured and hot isostatic pressed (HIP) samples. The CT analysis of the turbocharger wheel confirms that complex geometries made of TiAl can be additively manufactured free of cracks.

This content is only available via PDF.
You do not currently have access to this content.