Thermal Fatigue Testing of Plasma Transfer Arc Stellite Coatings on Hot Work Tool Steels under Steel Thixoforming Conditions

Birol, Yücel; Kayihan, A.B.

doi:10.1007/s11661-010-0473-2

Cited by 5 publications

(3 citation statements)

References 59 publications

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“…Improving tool service life has thus been a priority in the metalworking industry. Surface engineering methods [4][5][6][7][8][9][10][11][12][13][14] such as plasma nitriding have been popular. Plasma-nitriding [15] offers shorter treatment times, lower temperatures than traditional salt-bath-and gas-nitriding at a competitive cost for a wide range of steel grades.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Isothermal and Cyclic Oxidation of Plasma-Nitrided Hot-Work Tool Steel at Elevated Temperatures

Birol

2011

Oxid Met

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The oxidation of a plasma-nitrided, hot-work tool steel at temperatures that cover a range of operations from post-plasma-nitriding oxidation to steel thixoforging processing was investigated. Thermal exposure at 500°C led to the formation of a thin Fe-Cr spinel layer and an even thinner outermost layer of hematite. The former is the only oxide that grew on samples exposed to oxygen-lean conditions at 750°C. A thick, multi-layered oxide scale formed on the surface when the plasma nitrided hot-work tool steel was held at 750°C under atmospheric conditions. In this scale, the outermost hematite layer and the inner Fe-Cr spinel were separated by a magnetite layer. The oxide scale produced during thermal cycling at 750°C was also multi-layered with an identical oxide scale configuration to that formed during isothermal exposure at 750°C. The hematite layer, which retained its integrity during isothermal exposure at 750°C, suffered small cracks that were instrumental in its fracture and spallation during thermal cycling. The distinct feature resulting from cyclic oxidation, however, was the wide gap that formed along the magnetite-spinel interface. Thermal expansion mismatch produced compressive stresses which in turn led to buckling of the magnetite layer and to its detachment; while, the spinel layer adhered to the tool steel substrate and survived throughout thermal cycling. Enrichment of nitrogen and the subsequent precipitation of N 2 gas were also believed to have contributed to the gap formation. Formation of such a gap poses a serious threat to the integrity of the oxide scale and was shown to be responsible for the spallation of the magnetite layer upon thermal cycling.

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Section: Introductionmentioning

confidence: 99%

Investigation of Isothermal and Cyclic Oxidation of Plasma-Nitrided Hot-Work Tool Steel at Elevated Temperatures

Birol

2011

Oxid Met

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“…The temperature drop thus obtained was reported to be as much as 170°C for 150 lm thick YSZ coatings ( Ref 11). The same approach may be the sought-after solution to tooling problems encountered in steel thixoforming which uses semi-solid steel slugs preheated to at least 1300°C (Ref [12][13][14][15][16]. Investigations with oxide-based coatings for this particular application have shown encouraging results (Ref 17).…”

Section: Introductionmentioning

confidence: 99%

Thermal Cycling of Yttria-Stabilized Zirconia-Coated Hot Work Tool Steel

Birol

2011

J Therm Spray Tech

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Thermal fatigue performance of yttria-stabilized zirconia-coated hot work tool steel was investigated under conditions encountered by thixoforming dies in semi-solid processing of steels. The thermal barrier effect of the YSZ coating was evident from the relatively smaller and more uniform temperature gradients set up across the section of the sample, which in turn, had a direct impact on the magnitude of thermal stresses generated at the surface of the tool steel. In spite of some thermal expansion mismatch with the substrate tool steel and occasional discontinuous thermally grown oxides along the splat boundaries and between the BC and TC, the YSZ coating survived thermal cycling under steel thixoforming conditions for over 12,000 cycles with no evidence of debonding and spallation. This is a nearly ten-fold increase in thermal fatigue life with respect to the uncoated counterpart. An increasingly dense YSZ layer and the toughening linked with the tetragonal to monoclinic ZrO 2 phase transformation are credited for the remarkable performance of the YSZ-coating. It is fair to conclude that the YSZ coating offers adequate protection for the underlying tool steel, which without YSZ coating, suffers severe oxidation after only several hundred cycles and extensive cracking after 1000 cycles.

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“…There have been several attempts to explore the potential of PVD coatings in thixoforming tools [14,[16][17][18][19]. The latter are relatively softer and soften further upon thermal cycling at steel thixoforming temperatures [22]. It was thus concluded that thin hard coatings for steel thixoforming tools must be employed as duplex coatings via plasma nitriding followed by physical vapour deposition.…”

Section: Introductionmentioning

confidence: 99%

Thermal Fatigue Testing of Duplex-Coated Hot Work Tool Steels at Elevated Temperatures

Birol¹

2011

AIP Conference Proceedings

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Thermal fatigue is one of the principal failure mechanisms in thixoforming dies. PVD coatings provide adequate protection against oxidation of hot work tool steels but fail to improve thermal fatigue resistance. The extensive softening of the tool steel substrate and the thermal expansion mismatch between the hot work tool steel and the PVD coatings are held responsible. Hot work tool steel samples were plasma nitrided before coating with CrN/AlTiN using the Cathodic Arc Physical Vapour Deposition process. The duplex-coated samples thus obtained were submitted to thermal cycling under conditions which approximate thixoforming of steels. Plasma nitriding before PVD provides the much needed substrate support and has a very favourable impact on the thermal fatigue performance of the tool steel. The results from the thermal fatigue tests of the duplex-coated tool steel samples will be discussed and compared with tool steel samples coated via PVD alone.

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Thermal Fatigue Testing of Plasma Transfer Arc Stellite Coatings on Hot Work Tool Steels under Steel Thixoforming Conditions

Cited by 5 publications

References 59 publications

Investigation of Isothermal and Cyclic Oxidation of Plasma-Nitrided Hot-Work Tool Steel at Elevated Temperatures

Investigation of Isothermal and Cyclic Oxidation of Plasma-Nitrided Hot-Work Tool Steel at Elevated Temperatures

Thermal Cycling of Yttria-Stabilized Zirconia-Coated Hot Work Tool Steel

Thermal Fatigue Testing of Duplex-Coated Hot Work Tool Steels at Elevated Temperatures

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