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The Drivetrain Reliability Collaborative holds annual meetings convened by the National Renewable Energy Laboratory, Argonne National Laboratory, and the U.S. Department of Energy to bring researchers and stakeholders throughout the wind turbine drivetrain supply, operations, and sustainment chain together to explore the state of the art in mechanical system reliability and operations and maintenance challenges that if solved could have significant benefits. Identification of these research and development opportunities are a prime focus of the meetings and are summarized in this report.

The microstructures of Ti-6Al-4V following laser processing depend primarily on the phase transformation of β to α, but their development is constrained by the rapidly changing temperature in the small fusion zone. In-situ synchrotron X-ray diffraction was utilized to probe the rapid phase evolution in single melt tracks with high angular and temporal resolution. Both fully martensitic and mixed α+α'+β microstructures were confirmed by microscopy. Cooling rates were inferred from the lattice parameter history and complementary thermal simulation. It was found that the threshold cooling rate for fully martensitic transformation is in the range between 2900 and 6500°C/s. High-speed synchrotronmore » X-ray diffraction during operando laser processing suggests a new threshold between martensitic and diffusional phase transformation in Ti-6Al-4V occurring at higher cooling rates than previously reported.« less

The laser melting process is accompanied by rapid evolution in temperature, phase, structure, and strain because of its high heating and cooling rates. In this study, the evolution of grains within a thin solid plate of Ni alloy 718 during laser processing was probed with in situ high-energy x-ray diffraction experiments. The high temporal and spatial resolution available in the measurement allowed us to study the rapid evolution of the melted region beneath the surface of the sample. The characterization of the evolution of secondary phases, i.e., Laves and carbide, was captured despite the weak diffracted peaks caused by smallmore » volume fractions. Thermal history was estimated based on changes in the lattice spacing from the thermal contraction upon cooling. The temporal variation in 2θ with azimuthal direction revealed the evolution in anisotropy of lattice spacing and thus of the mechanical state during laser processing.« less

Laser powder bed fusion is a metal additive manufacturing technique that has received significant scientific and industrial attention over the past decades. However, the quality and reproducibility of parts manufactured by this technique is still a problem. Overcoming this issue requires an understanding of multiple complex physical phenomena which occur simultaneously during the process. Here, we illustrate a powerful new technique which synchronizes high-speed x-ray imaging with high-speed infrared imaging to study laser powder bed fusion processes in real time. Using this technique, we demonstrate the simultaneous observation of multiple phenomena including three-dimensional melt pool visualization, vapor plume dynamics, spattermore » formation, thermal history, and point cooling rates. The paired observation of these dynamic phenomena is critical to understanding the fundamentals of laser powder bed fusion, and the overall impact of process parameters on print quality.« less

White etching cracks (WECs) are the dominant mode of failure for wind turbine gearbox bearings. These failures are characterized by subsurface initiation and local region of microstructural alterations adjacent to the crack faces. The definitive cause of WECs within the field is unknown, because of this laboratory replication has proved difficult. At a benchtop scale, specific lubricant formulations referred to as bad reference oils (BROs) are often employed to aid in the formation of WECs; however, exactly how these lubricants induce WECs is unknown. The present work intends to elucidate how these lubricants facilitate the formation of WECs by systematicallymore » varying the additives which are found in BROs and studying the effect that these additive combinations have on time until failure, as well as tribofilm development. It was found that the lubricant containing Zinc dialkyldithiophosphate alone led to the formation of WECs sooner than any lubricant studied. It was also documented that a lubricants frictional characteristics play a more dominant role than the tribofilm characteristics.« less

Crack surrounded by local areas of microstructural alteration deemed "White etching cracks" (WECs) lead to unpredictable and premature failures within a multitude of applications including wind turbine gearbox bearings. While the exact cause of these failures remains unknown, a large number of hypotheses exist as to how and why these cracks form. The aim of the current work is to elucidate some of these hypotheses by mapping WEC networks within failed wind turbine bearings using high energy X-ray tomography, in an attempt to determine the location of WEC initiation, and the role of defects within the steel, such as inclusionsmore » or carbide clusters. Four completely subsurface WECs were found throughout the presented analysis, thereby confirming subsurface initiation as method of WEC formation. Additionally, a multitude of small butterfly like cracks were found around inclusions in the steel, however further analysis is needed to verify if these inclusions are initiation sites for WECs. (C) 2017 Elsevier Ltd. All rights reserved.« less

White etching cracks (WECs) have been identified as a dominant mode of premature failure within wind turbine gearbox bearings. Though WECs have been reported in the field for over a decade, the conditions leading to WECs, and the process by which this failure culminates, are both highly debated. In previously published work, the generation of WECs on a benchtop scale was linked to sliding at the surface of the test sample, it was also postulated that the generation of WECs was dependent on the cumulative energy that had been applied to the sample over the entirety of the test. Inmore » this paper, a three ring on roller bench top test rig is used to systematically alter the cumulative energy that a sample experiences through changes in normal load, sliding, and run time, in an attempt to correlate cumulative energy with the formation of WECs. It was determined that, in the current test setup, the presence of WECs can be predicted by this energy criterion. The authors then used this information to study the process by which WECs initiate. Lastly, it was found that, under the current testing conditions, the formation of a dark etching microstructure precedes the formation of a crack, and a crack precedes the formation of white etching microstructure.« less

White etching cracks (WECs) have been identified as the dominant mechanism of premature failure for bearings within wind turbine gearboxes. Though WECs have been observed in the field for over a decade, the exact mechanisms which lead to this failure are still debated, and benchtop replication has proven difficult. In previously published work, WECs have been replicated only through the use of component level test rigs, where complete bearings are tested. In these tests, the factors that are thought to drive the formation of WECs, such as slide-to-roll ratio (SRR) and lubricant film thickness, cannot not be easily altered ormore » controlled. In this paper, WECs have been replicated on a three rings on roller, benchtop test rig, which allowed for a direct investigation into the influence that SRR magnitude, sliding direction, and the lubricant film thickness have on surface failures and WEC generation. It was determined that WEC were formed in samples that experienced -30% SRR at various lubrication conditions, however, at lower levels of negative SRR and positive SRR up to 30% no white-etching cracks were observed.« less