In-Wook Park

Deposition and mechanical evaluation of superhard Ti–Al–Si–N nanocomposite films by a hybrid coating system

New superhard TiAlSiN films, characterized by a nanocomposite comprising nano-sized (Ti,Al,Si)N crystallites embedded in amorphous Si3N4 matrix, could be successfully synthesized on WCCo substrates by a hybrid coating system of arc ion plating (AIP) and sputtering method. The hardness and Youngs modulus value of the TiAlSiN film increased with incorporation of Si, and had the maximum value of ∼55 GPa and ∼650 GPa at the Si content of 9 at.%, respectively. The average friction coefficient of the TiAlSiN films largely decreased with an increase of the Si content. This behavior would be attributed to the tribo-chemical reaction between Si and ambient humidity, which enabled to form SiO2 or Si(OH)2 tribo-layer playing a role as self-lubricant. The harder TiAlSiN film was found to be more wear-resistant against steel. A systematic work on the microstructure and mechanical properties of TiAlSiN films is reported in this paper.

A study on a die wear model considering thermal softening: (I) Construction of the wear model

The service life of tools in metal forming process is to a large extent limited by wear, fatigue fracture and plastic deformation. In elevated temperature forming processes wear is the predominant factor for tool operating life. To predict tool life by wear Achards model is generally applied. Usually hardness of die is considered to be a function of temperature. But hardness of die is a function of not only tem-perature but also operating time of die. To consider softening of die by repeated operation it is necessary to express hardness of die by a function of a function of temperature and time. By experiment of reheating of die softening curve was obtained and applied to suggest modified Archards Model in which hardness is a function of main tempering curve.

A study on die wear model considering thermal softening (II): Application of the suggested wear model

In bulk metal forming processes prediction of tool life is very important for saving production cost and achieving good material properties. Generally the service life of tools in metal forming process is limited to a large extent by wear, fracture and plastic deformation of tools. In case of hot and warm forging processes tool life depends on wear over 70%. In this study finite element analyses are con-ducted to warm and hot forging by adopting suggested wear model. By comparison of simulation and eal profile of die suggested wear model. By comparison of simulation and real profile of die suggested model is verified.

Effects of Si addition on the microstructural evolution and hardness of Ti–Al–Si–N films prepared by the hybrid system of arc ion plating and sputtering techniques

Ti–Al–Si–N films were deposited on WC–Co substrates by the hybrid coating system of arc ion plating method for Ti–Al sources and dc magnetron sputtering technique for Si incorporation. The synthesized Ti–Al–Si–N films were revealed as composites of solid-solution (Ti,Al,Si)N crystallites and amorphous Si3N4 by instrumental analyses such as x-ray diffraction, high-resolution transmission electron microscopy, and x-ray photoelectron spectroscopy. The Si addition in Ti–Al–N films affected the refinement and uniform distribution of crystallites by percolation phenomenon of amorphous silicon nitride similar to that of the Si effect in TiN film. The solubility limit of Si in the Ti0.76Al0.24N crystal is believed to be about 6 at. %. No free Si was observed due to the very high ionization rate of nitrogen gas in the arc plasma. As the Si content increased up to about 9 at. %, the hardness of Ti–Al–N film steeply increased from 30 GPa to about 50 GPa. Ti–Al–Si–N films having the maximum hardness showed the nanoco...

Effects of bias voltage and temperature on mechanical properties of Ti-Si-N coatings deposited by a hybrid system of arc ion plating and sputtering techniques

Abstract Ti–Si–N coatings were deposited on WC–Co substrates by a hybrid coating system of arc ion plating (AIP) and sputtering techniques. Effects of deposition temperature and substrate bias voltage on the microstructure and mechanical properties, such as microhardness, indentation elastic modulus of Ti–Si–N coatings were systematically investigated in this work. As the deposition temperature increased up to 300 °C, microhardness and indentation elastic modulus of the Ti–Si–N coating steadily increased. Higher temperature above 350 °C, however, caused the microhardness to decrease due to grain growth. The substrate bias voltage had an effect on the Si content in Ti–Si–N coating. Applying a small substrate bias voltage of −100 V in Ti–Si–N coatings induced compressive residual stress into the coating and modified its microstructure toward denser one due to ion bombardment effect. However, much higher substrate bias voltage of −400 V caused the diminution of Si content by re-sputtering phenomenon, which could result in a decline of nanocomposite characteristics of Ti–Si–N. The superior mechanical properties of the Ti–Si–N coatings were obtained at the deposition condition of 300 °C, −100 V.

Microstructure and mechanical properties of superhard Ti–B–C–N films deposited by dc unbalanced magnetron sputtering

Superhard quarternary Ti–B–C–N films were successfully deposited on AISI 304 stainless steel substrates by a dc unbalanced magnetron sputtering technique from a Ti–B–C composite target. The relationship between microstructures and mechanical properties was investigated in terms of the nanosized crystallites∕amorphous system. The synthesized Ti–B–C–N films were characterized using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). These analyses revealed that our Ti–B–C–N films are composites of solid-solution (Ti,C,N)B2 and Ti(C,N) crystallites distributed in an amorphous boron nitride (BN) phase including some of carbon, CNx, B2O3 components. The hardness of the Ti–B–C–N films increased with the increase of N content up to a maximum value of approximately 45 GPa at 10 at. % N, with a subsequent decrease in hardness at higher N content. This value is considerably higher than the hardness measured in our Ti–B–C films (∼35GPa). The Ti–B–C–N(10 at .%)...

Performance evaluation of AIP-TiAlN coated tool for high speed machining

Abstract Ti 0.67 Al 0.33 N single-layered and Ti 0.52 Al 0.48 N/TiN double-layered coatings were applied to end-mill tools made of WC–Co material by an arc ion plating technique. Their performances under high speed cutting conditions were evaluated about cutting force, tool wear, and surface roughness of workpiece. With Ti–Al–N coatings, tool life and performance were much increased under high speed machining. The Ti 0.67 Al 0.33 N single-layer coated tool showed higher wear-resistance due to its higher hardness, while the Ti 0.52 Al 0.48 N/TiN double-layer coated tool showed better performance for high metal removal, i.e., high feed per tooth condition due to its higher toughness. The surface roughness of the workpiece was not influenced by the wear of coated tools. It was, however, increased as the experimental conditions became severe, i.e., with increases of cutting speed and feed per tooth. An integrated evaluation system for cutting tools was introduced in this work.

Influence of substrate bias voltage on deposition behavior and micro-indentation hardness of Ti–Si–N coatings by a hybrid coating system of arc ion plating and sputtering techniques

Abstract In this work, the influence of substrate bias voltage on deposition behaviors such as deposition rate, film composition, macroparticles and surface roughness were investigated for the Ti–Si–N coatings deposited on WC–Co substrates by a hybrid coating system of arc ion plating and sputtering techniques. Also, the hardness and Youngs modulus of Ti–Si–N coatings by nanoindentation tests were investigated with the substrate bias voltage. Applying substrate bias voltage up to −100 V during Ti–Si–N deposition resulted in the significant diminution of macroparticles and smoothening of surface morphology. The micro-indentation hardness and Youngs modulus values were also significantly increased at a bias voltage of −100 V, and showed the highest values of ∼60 and ∼700 GPa, respectively. However, increasing the negative bias voltage above −100 V caused the continual reduction of those properties, and reduced both deposition rate and Si content in the Ti–Si–N coatings.

FE program development for predicting thermal deformation in heat treatment

Abstract The distortion or fracture of heat treated components is a major industrial problem, which may considerably increase the costs of operations and decrease the qualities of core parts. In heat treatment industrial fields, the methods used to control these undesirable effects have been necessarily empirical. Therefore, these problems could not be handled systematically and did not be studied quantitatively. To predict thermal deformation of final shape after heat treatment, many factors related to heat treatment process and thermal analysis must be considered. In the present study, the purpose is development of a FE program to predict and control thermal deformation. The program could analyze heat treatment process by calculating temperature, thermal stress and deformation value. The two-dimensional program based on finite element method has been developed and it is applied to actual heat treatment process. Actual heat treatment process (TD process) has been applied to predict thermal deformation by comparison of several experiment data and simulations.

Influence of N2 gas pressure and negative bias voltage on the microstructure and properties of Cr–Si–N films by a hybrid coating system

Cr–Si–N films were deposited using a hybrid coating system combining arc ion plating and magnetron sputtering. The authors investigated the influence of N2 flux rate and negative bias voltage on the microstructure and properties of Cr–Si–N films, e.g., chemical composition, film morphology, phase structure, residual stress, and microhardness. The results showed that all the Cr–Si–N films were close to stoichiometry. The N2 flux rate had no important influence on the microstructure and properties of the Cr–Si–N films. Applying a negative bias voltage resulted in significant decrease in macroparticle densities and smoother film surface. Also the film microstructure transformed from apparent columnar to nanocomposite microstructure. The maximum microhardness obtained ranged from 45to50GPa at a bias voltage ranging from −50to−100V. The microhardness enhancement could be ascribed to the mixed effect of grain size diminishment and residual compressive stress.