Microstructure tribological performance and anti-oxidation properties of tungsten coatings with various alloying elements (C Ti Cr or Al)

  • 林 岳鋒

Student thesis: Doctoral Thesis

Abstract

A closed field unbalanced magnetron sputtering (CFUBMS) system is used to deposit tungsten coatings with various contents of carbon titanium chromium and aluminum (W-Cx% W-Tix% W-Crx% and W-Alx%) on SKH51 high-speed steel substrates The chemical compositions of the various coatings are analyzed by energy dispersive X-ray spectrometry (EDX) and glow discharge spectrometry (GDS) In addition the microstructures of the as-deposited coatings are examined by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) The adhesion strengths of the coatings are characterized by scratch tests The hardness and elastic modulus properties of the coatings are evaluated by nanoindentation testing Finally the tribological properties of the various coatings are investigated using a pin-on-disc tribometer under dry conditions Having characterized the coatings in an as-sputtered condition the oxidation resistance mechanical properties and tribological properties of the coatings in a high-temperature environment are observed after oxidation testing Finally the practical applicability of the various coatings is examined by means of turning tests and PCB micro-drilling tests The experimental results show that among the as-deposited W-Cx% coatings the W-C41% coating possesses the highest hardness (25 2 GPa) Moreover the optimal wear resistance is obtained given a C content of 28 at % For the W-Tix% coatings the W-Ti5% coating possesses both the highest hardness (23 8 GPa) and the best wear resistance Similarly among the W-Crx% coatings 31 at % Cr addition yields both the highest hardness (19 5 GPa) and the best wear resistance Finally for the W-Alx% coatings the coating with 15 at % Al yields both the highest hardness (15 1 GPa) and the best wear resistance Overall the results suggest that the H/E ratio of the coatings (where H is the hardness and E is the elastic modulus) is directly related to the wear resistance For example the W-C28% coating has the highest H/E ratio (0 065) of the various coatings and provides the best tribological performance Following the oxidation tests at 500°C and 600°C respectively the W-C28% and W-Ti5% coatings have a poor mechanical and tribological performance Moreover the oxidation resistance of the W-Cr31% and W-Al15% coatings is better than that of the W-C28% and W-Ti5% coatings The W W-C28% W-Ti5% W-Cr31% and W-Al15% coatings are coated on WC-Co inserts and micro-drills and used to perform a series of turning and drilling tests In the turning tests the W-C28% coated insert reduces the flank wear by 59% compared with an uncoated insert Moreover in the PCB micro-drilling tests the W-C28% coated micro-drill reduces the flank wear by 49% and the corner wear by 56% compared with an uncoated drill
Date of Award2016 May 10
Original languageEnglish
SupervisorYean-Liang Su (Supervisor)

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