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The exhaust valve spindle is one of the most challenging components in the marine two-stroke diesel engine. It has to withstand high mechanical loads, thermal cycling, surface temperatures beyond 700 degrees C, and molten salt induced corrosion. Powder metallurgy gives the opportunity of improving the component using materials not applicable by welding or forging. Therefore exhaust valve spindles have been produced by Hot Isostatic Pressing (HIP) with a spindle disc coating of a Ni-Cr-Nb alloy that cannot be manufactured by welding or forging. This paper presents the service experience gathered by MAN Diesel & Turbo in a number of service tests on ships (up to 18000 running hours): corrosion and degradation phenomena in the spindles produced by HIP are presented and compared with the performance of state-of-the-art exhaust valve spindles. The macroscopic geometrical changes experienced by the spindles are studied by means of Finite Element Method (FEM) calculations and strategies for further development of the component are outlined.

Additive Manufacturing (AM) enables the design of complex part geometries for high-temperature applications. Laser Powder Bed Fusion or Direct Energy Deposition of the nickel-based superalloy MAR-M247 poses a challenge in AM due to its poor weldability. Binder Jetting does not utilize a heat source and interaction with a liquid metal during build-up and thus has the potential to overcome this limitation. In this study, MAR-M247 was manufactured by Binder Jetting and subsequently characterized regarding density and microstructure. Combinations of two different Hot-Isostatic-Pressing (HIP) treatments (T = 1120–1180 °C, p = 1000–1500 bar, t = 4 h) and four different heat-treatments involving solution treatment (T = 1250 °C, t = 4 h) and different aging steps (T = 700–1000 °C, t = 12–24 h) were applied to study the densification and microstructural evolution of binder-jetted MAR-M247. The influence of the build direction in combination with HIP is studied concerning the resulting density and mechanical properties at room temperature. The results show that close-to-full densification can be achieved after HIP. Subsequent solution treatment and double-aging after HIP lead to a favorable bimodal microstructure. A process chain for binder-jetted MAR-M247 is presented, which yields tensile properties comparable to those of analogously post-processed cast material. Further possibilities of microstructural optimization and the design philosophy are discussed in the light of the Binder Jetting process-chain.

Metal additive manufacturing is highly suited to enhance the performance of engineering applications with sophisticated internal features and passageways. Laser Powder Bed Fusion (LPBF) is commonly used or considered for fabrication in these applications, although the resulting channels can show significant form and surface deviations, particularly due to dross-formation at overhang-areas. Binder Jetting (BJ), another additive manufacturing method that can process metals does not employ a heat source to fuse powder particles during build-up and therefore has the potential to overcome these limitations. In this study, additively manufactured circular channels with a nominal diameter of two millimeters are made by LPBF and BJ in seven different directions and are extensively analyzed depending on their orientation. The test-artifacts are made by four different state-of-the-art LPBF and BJ system manufacturers with standard parameters in 17−4PH stainless steel and with similar layer thicknesses. A novel type of X-ray Computed Tomography (CT) image analysis method for additively manufactured channels is applied in combination with commercial image analysis software. Form deviations and surface texture are characterized in accordance with ISO1101 and ISO 4287:1997. Results show a high level of precision, independently of build direction for channels made by BJ when compared to LPBF. The accuracy of BJ-channels is strongly dependent on the appropriate scaling before printing. Parallel to the build direction, LPBF-channels exhibit superior characteristics. The channels investigated in this work are categorized into ISO tolerance grades IT13−17 for LPBF and IT13−15 for BJ following ISO268−2. Based on the findings, design considerations and characteristic attributes of each process to manufacture channels are discussed within a broader context.

Electrochemical reactors operating at intermediate temperatures (200 – 400 °C) can potentially have several advantages over their high temperature (600- 1000 °C) and low temperature (< 100 °C) counterparts. For example their potential of an increased catalytic activity enabling a decrease in material cost compared to low temperature cells, and can be thermally integrated into other chemical processes like synthesis of synthetic fuels and chemicals, such as methanol and ammonia. Electrochemical reduction of CO2 to chemical building blocks such as CO, CH3OH, and CH4 is a dream for electrochemists, and high faradaic efficiencies have been reported for liquid electrochemical cells operated at ambient temperature, using e.g. Cu electrodes [1]. However, selectivity and electrochemical activity are far from being technically relevant, so that heterogeneous catalysis processes still are the matter of choice. Even more difficult is the electrochemical reduction of nitrogen f.i. to ammonia. In this contribution, activities at DTU Energy are summarized using solid state electrochemical cells under operating conditions close to the well-known catalytic synthesis of methanol and ammonia. For CO2 reduction, cells based on CsH2PO4 as electrolyte and Cu based cathodes have been investigated towards their electrochemical activity in both H2/H2O and H2/H2O/CO2 containing atmospheres at elevated temperatures of 240 °C. Proton conducting ceramics cells based on barium cerate with Mo and Fe electrodes have been characterized in H2/N2 atmospheres between 300 and 500 °C. Electrochemical impedance analysis point towards a predominant hydrogen evolution and the role of adsorption and desorption processes as well as overpotential will be discussed. [1] Y. Hori, Modern Aspects of Electrochemistry: Electrochemical CO2 Reduction on Metal Electrodes, Springer New York, USA 42 (2008), 89-189.

The synthesis of titanium pyrophosphate is carried out, and the material is sintered at different temperatures between 370 and 970 °C. Yttrium is added during the synthesis to act as acceptor dopant, but it is mainly present in the material in secondary phases. The conductivity is studied systematically as a function of sintering temperature, pH2O, pO2, and temperature (100–400 °C). Loss of phosphorus upon sintering above 580–600 °C is confirmed by energy dispersive spectroscopy and combined thermogravimetry and mass spectrometry. The conductivity decreases with increasing sintering temperature and decreasing phosphorus content. The highest conductivity is 5.3 × 10−4 S cm−1 at 140 °C in wet air (pH2O = 0.22 atm) after sintering at 370 °C. The conductivity is higher in wet atmospheres than in dry atmospheres. The proton conduction mechanism is discussed, and the conductivity is attributed to an amorphous secondary phase at the grain boundaries, associated with the presence of excess phosphorus in the samples. A contribution to the conductivity by point defects in the bulk may explain the conductivity trend in dry air and the difference in conductivity between oxidizing and reducing atmospheres at 300–390 °C. Slow loss of phosphorus by evaporation over time and changes in the distribution of the amorphous phase during testing are suggested as causes of conductivity degradation above 220 °C.

A two-step doping strategy was applied to the synthesis of La0.9Sr0.1Ga0.8Mg0.2O2.85(LSGM1020) powder by a gel combustion method. The Mg-doped LaGaO3 powder was prepared in the first step, and Sr i ...

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