Full-Scale Testing of the Fatigue Life of Laser Additive Manufacturing Repaired Alloy Steel Components

• Author / Creator

  Bell, Kurtis P.

• Laser additive manufacturing, or laser cladding, is a weld overlay technique that is being increasingly used for hardfacing and corrosion resistant overlays and dimensional repairs of oil and gas, petrochemical, and mining components. However, laser cladding's use in industry is currently limited to non-critical applications due to a lack of applicable information on how laser cladding affects the fatigue life of industrial components. In this investigation, the effect of laser cladding is assessed on 2.750 inch (69.85 mm) diameter components. The material system comprises wrought quenched and tempered AISI-SAE 4140H steel overlaid with 13Cr steel, which is representative of refurbished driveshafts used in the upstream oil and gas and mining industries. The specimens were evaluated in four point rotating bending fatigue on a custom built apparatus. The effect of utilizing no preheat, 300°F (149°C), and 600°F (316°C) preheats were evaluated relative to unclad 4140H steel (control condition) using a randomized complete block experimental format. The fatigue results were analyzed using the Kaplan-Meier survival analysis and the log-rank test. It was determined that laser cladding with a 300°F (149°C) or 600°F (316°C) preheat increases the fatigue life relative to unclad 4140H, or 4140H clad without the use of a preheat, at the 95.5% confidence interval. The impact of laser cladding operations on the fatigue life of the samples was characterized through fractography, hardness surveys, and residual stress measurements by the hole drilling method. It was determined that the laser applied overlays, regardless of preheat level, had higher measured hardness than the unprocessed 4140 (overlay: HVNo Preheat = 418, HV300°F = 399, HV600°F = 430, 4140 substrate HV = 294). Laser processing of the samples was also found to induced large compressive residual stress states that were greater than 60% of the substrate yield stress. The increase in fatigue performance following laser cladding with a suitable preheat is attributable to two factors: the large compressive residual stresses induced during laser operations, and the higher hardness of the overlay relative to the substrate material. The induced compressive residual stresses reduce the tensile stress applied during testing, and create a lower effective stress state in the near surface region of the samples. The higher hardness of the overlay indicates a higher degree of resistance to the presence of discontinuities than the base material in regimes where the fatigue strength is dominated by material defects.

• Subjects / Keywords

  • Full Scale
  • Laser Cladding
  • Kaplan-Meier
  • Laser Additive Manufacturing
  • Fatigue

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3251G01V

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.