C. Kenel

Processing of metal-diamond-composites using selective laser melting

Purpose – The purpose of this paper is a feasibility study that was performed to investigate the basic processability of a diamond-containing metal matrix. Powder-bed-based additive manufacturing processes such as selective laser melting (SLM) offer a huge degree of freedom, both in terms of part design and material options. In that respect, mixtures of different powders can offer new ways for the manufacture of materials with tailored properties for special applications such as metal-based cutting or grinding tools with incorporated hard phases. Design/methodology/approach – A two-step approach was used to first investigate the basic SLM-processability of a Cu-Sn-Ti-Zr alloy, which is usually used for the active brazing of ceramics and superhard materials. After the identification of a suitable processing window, the processing parameters were then applied to a mixture of this matrix material with 10-20 volume per cent artificial, Ni-coated mono-crystalline diamonds. Findings – Even though the processing...

In situ investigation of phase transformations in Ti-6Al-4V under additive manufacturing conditions combining laser melting and high-speed micro-X-ray diffraction

We present combined in situ X-ray diffraction and high-speed imaging to monitor the phase evolution upon cyclic rapid laser heating and cooling mimicking the direct energy deposition of Ti-6Al-4V in real time. Additive manufacturing of the industrially relevant alloy Ti-6Al-4V is known to create a multitude of phases and microstructures depending on processing technology and parameters. Current setups are limited by an averaged measurement through the solid and liquid parts. In this work the combination of a micro-focused intense X-ray beam, a fast detector and unidirectional cooling provide the spatial and temporal resolution to separate contributions from solid and liquid phases in limited volumes. Upon rapid heating and cooling, the β ↔ α′ phase transformation is observed repeatedly. At room temperature, single phase α′ is observed. Secondary β-formation upon formation of α′ is attributed to V partitioning to the β-phase leading to temporary stabilization. Lattice strains in the α′-phase are found to be sensitive to the α′ → β phase transformation. Based on lattice strain of the β-phase, the martensite start temperature is estimated at 923 K in these experiments. Off-axis high speed imaging confirms a technically relevant solidification front velocity and cooling rate of 10.3 mm/s and 4500 K/s, respectively.

Integrating Fiber Fabry-Perot Cavity Sensor Into 3-D Printed Metal Components for Extreme High-Temperature Monitoring Applications

This paper reports the methods of embedding into 3-D printed metal components a fused silica capillary designed to accept an in-fiber Fabry–Perot cavity-based extreme high-temperature sensor. The components are manufactured in stainless steel (SS316) by additive manufacturing using selective laser melting (SLM). The temperature sensor consists of a standard single-mode optical fiber with the F-P sensor located at the distal end of the fiber with the fiber being inserted into the capillary. The capillary is either directly embedded into the structure during the SLM build process or brazed into the structure in between the SLM build process, and the advantages and disadvantages of these two manufacturing approaches are discussed. Temperature sensing of up to 1000 °C inside the metal with an accuracy better than ±10 °C is reported. The capillary can be directly embedded in the component, which needs to be monitored, or it can be embedded in a metal coupon, which can be attached to a component by conventional welding technology, including the use of laser metal deposition (LMD). In the case of LMD, the sensor coupon can also be fully encapsulated by over cladding the coupon.

In Situ and Real-Time Monitoring of Powder-Bed AM by Combining Acoustic Emission and Artificial Intelligence

At present, the quality control in additive manufacturing is diligently based on temperature of the process zone or high resolution imaging. Hence, various sensors such as pyrometers, photo diodes and matrix CCD detectors are used. The discrepancies in temperature measurements and the real temperature distribution inside the powder medium reduce the reliability of this method. The high resolution imaging monitors the quality post factum, after a part is manufactured. So far, no methods are known to monitor the quality of additive manufacturing in situ and in real-time. To achieve the goal of accurate real-time quality control, we propose an approach that relies on acoustic emission, which is further analyzed within artificial intelligence framework. We show that the additive manufacturing process has a number of unique acoustic signatures that can be detected, extracted and interpreted in terms of quality.

High temperature isothermal oxidation behaviour of an oxide dispersion strengthened derivative of IN625

Abstract Gas atomised IN625 powder was mechanically alloyed with <1·0 Wt.% nano-yttria and consolidated by spark plasma sintering (SPS) to produce an oxide dispersion strengthened (ODS) alloy. The isothermal oxidation rate constant of the ODS alloy, and wrought IN625, was determined by thermogravimetric analysis. This was performed at 900 °C in static laboratory air for exposure times of up to 1000 h. It was found that the ODS alloy oxidised ~40x slower than wrought IN625, which is attributed to the reactive element effect. It is further proposed that the improvement in oxidation resistance of the ODS alloy, and the superior morphology of the oxide scale formed on the ODS alloy, may be related to the presence of Nb carbide, rather than δ-phase, in the ODS alloy.