Cheng-n Hsu

Effects of PVD sputtered coatings on the corrosion resistance of AISI 304 stainless steel

Abstract This research studied the corrosion resistance enhancement of AISI 304 stainless steel by utilizing TiCN, CrN, and DLC films deposited by means of physical vapor deposition (PVD). The corrosion media used were NaCl, HCl, and H 2 SO 4 aqueous solutions, respectively. The results showed that all PVD coating types reduced the corrosion current thus providing better corrosion resistance. Among the three PVD films studied, DLC film gave the best results in all aqueous solutions. CrN film yielded a better corrosion resistance than TiCN in H 2 SO 4 solution, although both produced about the same effect in HCl and NaCl solutions.

Synthesis of (Ti, Zr)N hard coatings by unbalanced magnetron sputtering

Abstract In this study, ternary (Ti,Zr)N thin films were synthesized using unbalanced magnetron sputtering with pulsed substrate bias. The pulsed bias effectively eliminated the arcing damage caused by surface contaminants and oxides on the substrate. The results show that a solid solution of (Ti,Zr)N (evidence from XRD and TEM analysis) was formed at all deposit parameters in which the multicomponent Ti–Zr–N coatings were deposited. The (Ti,Zr)N grains are columnar and grow in the (111) orientation. The ternary (Ti,Zr)N coating demonstrates an enhanced microhardness compared with the binary TiN and ZrN coatings deposited under equivalent conditions. A better combination of condition of the values of microhardness and adhesion was obtained at OEM of 60% and bias of –70 V.

Study of high cycle fatigue of PVD surface-modified austempered ductile iron

Austempered ductile iron (ADI) is made from ductile iron by an austempering treatment, and its main microstructure is ausferrite that is composed of acicular ferrite and high carbon austenite. The purpose of this experiment is to investigate the influence of different coating layers and the size of casting (mass effect) on the high-cycle fatigue properties of ADI. Specimens in two casting sizes of the same chemical composition were subjected to a high-toughness austempering treatment, then coated with TiN or TiCN hard films by a physical vapor deposition (PVD) process. The results showed that the fatigue limit of the small casting size ADI is 292 MPa for ADI coated with TiN and 306 MPa for ADI coated with TiCN, which are 16% and 22%, respectively, higher than that of the ADI without coating (251 MPa). For the large casting size ADI, the fatigue limits are 200, 214 and 217 MPa for ADI without coating, ADI coated with TiN and ADI coated with TiCN, respectively. ADI coated with TiN and with TiCN are 7% and 9% better than the uncoated. Thus, it is concluded that TiN and TiCN coatings by PVD can improve the high-cycle fatigue strength of ADI. This is due to the high surface hardness and possibly the ADI surface compressive residual stress as well. For the small casting size ADI, TiCN-coated specimens have a bit higher fatigue strengths and this might be attributed to the higher hardness of TiCN than TiN films. As to the effect of mass, it is found that the small casting size has better fatigue properties and benefits more from the coating films. This could have stemmed from the higher nodule count and its associated benefits in thinner castings.

Effects of titanium addition and section size on microstructure and mechanical properties of compacted graphite cast iron

Abstract Titanium is an anti-spheroidizing element and also carbide former in ductile iron. On the other hand, increasing the casting size essentially lowers the cooling rate that opposes the chilling tendency of titanium. This research was to study the combined effects of titanium and section size on their promotion of compacted graphite (CG) formation, and at the same time how matrix constituents were altered in heavy-wall castings. It was found that at the increasing casting thickness of 30 mm, 65 mm and 80 mm, the percentage of CG increased while that of pearlite decreased either with or without titanium addition. However, titanium (added in an amount of 0.15 wt%) effectively promoted the formation of CG by over 10% and at the same time increased the pearlite content in the matrix. This was especially true in the thinner 30 mm casting. Irons with titanium addition exhibited a bit lower Brinell hardness, elongation, and impact toughness due probably to the higher CG percentage that facilitated easier crack propagation. However, comparing to the un-alloyed iron, fracture toughness increased along with tensile strength for iron with titanium addition in all casting sizes of 30–80mm. The higher pearlite content in the matrix has overridden the effect of increased CG percentage such that tensile strength and KIC value both increased.

Relationship Between Ultrasonic Characteristics and Mechanical Properties of Tempered Martensitic Stainless Steel

This research studied the relationship between the ultrasonic characteristics and the mechanical properties of tempered CA-15 martensitic stainless steel (MSS). The results show that, for as-quenched specimens, a chromium carbide film at the martensitic boundary of the as-cast specimen will disappear causing a change in the mechanical properties (e.g., the tensile strength is decreased or the hardness and the toughness are increased). For the tempered MSS, the correlation of the ultrasonic velocity and the tensile strength, hardness, and toughness is not obvious. However, there is a highly positive correlation with the elastic modulus (E) of the material. For the ultrasonic attenuation evaluation, the attenuation coefficient (α) has a positive correlation with the tensile strength and the hardness, while there is a negative correlation with the toughness and the elongation. Also, a higher-frequency probe would cause the better sensitivity, but the data are relatively dispersed.

Corrosion Resistance of Tool Steel Arc-Deposited Cr-N-O Double-Layered Coatings in 3.5% Sodium Chloride

Abstract In this study, the cathodic arc deposition technique was utilized to synthesize three Cr-N-O coatings (chromium nitride [CrN], CrN/Cr[N,O], CrN/chromium oxide [Cr2O3]) on AISI M2 tool steel by using the chromium target and controlling the flow rate of nitrogen/oxygen reactive gases. Polarization tests were performed to evaluate the corrosion resistance of the uncoated and coated specimens in 3.5 wt% sodium chloride (NaCl) solution. Structure and morphology of the coatings were separately analyzed using x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to better understand the coating effects on the corrosive behavior of M2 steel. The results showed that the CrN/Cr(N,O) and CrN/Cr2O3 double-layered coatings had higher surface roughness than monolithic CrN, but their dense and double-layered structures resulted in better corrosion resistance. The sequence of corrosion resistance is in the order of CrN/Cr(N,O) > CrN/Cr2O3 > CrN > uncoated M2 stee...

RETRACTED: Effects of PVD sputtered coatings on the corrosion resistance of AISI 304 stainless steel

Abstract This article has been retracted at the request of the editor. Reason: This article previously appeared in MSA 347/1–2 on pages 123–129. The reason for this is due to an error at the production stage where dual copies of the manuscript were held on file.

Study on Characteristics of ADI Coated DLC/ TiN /TiAlN Coatings by Cathodic Arc Evaporation

In this study, austempered ductile iron (ADI) substrate containing acicular ferrite and high-carbon austenite in the microstructure is made by austempering treatment at 360. Cathodic arc evaporation (CAE) coating technique was used to coat DLC, TiN and TiAlN films on ADI for surface modification. The results showed that the three coatings could be successfully coated onto ADI through CAE process without altering the unique microstructure of ADI. The structures of the coatings were identified by XRD, Raman and TEM, respectively. After HRC indentation testing, it was found that nodular graphite was the initial site of cracking for the coatings and then peeled. Surface roughness of all coated specimens was increased because the droplets generated on the substrate surface during the CAE process. Coated ADI had better wearability performance than uncoated ADI due to higher surface hardness. Coated specimens exhibited higher corrosion resistance than uncoated ones when they were immersed in separate solutions of both 3.5 wt. % NaCl and 10 vol. % HCl. In particular, TiAlN had the best corrosion resistance among the coated specimens.

Fracture mechanics behaviour of austenitic compacted graphite cast iron

The fracture mechanics behaviour of high-nickel austenitic compacted graphite cast iron was studied and the effects of graphite morphology, alloying elements and specimen thickness on the mechanical properties, plane stress fracture toughness, and fatigue crack growth rate were evaluated. It was found that the graphite morphology, i.e. the percentage of compacted graphite present, was the major determinant of all properties of the materials investigated. The irons with a greater amount of compacted graphite (the balance was nodular graphite in austenitic matrix) resulted in lower tensile strength, yield strength, elongation and Kc fracture toughness but higher crack-growth index values (poorer crack-growth resistance). For 25 mm thick specimens, Kc values of the austenitic compacted graphite cast irons in this study were in the range of 58–64 MPa m1/2. This is higher than ferritic/pearlitic ductile iron of 43–53 Mpa m1/2, and is compatible to Ni-resist austenitic ductile iron of 64.1 Mpa m1/2. The addition of cobalt not only contributed to slightly higher values of mechanical properties, but also higher plane stress fracture toughness and better crack growth resistance. Optical microscopy, scanning electron microscopy and X-ray diffraction techniques were applied to correlate the microstructural features to the properties attained.

Oxidation Resistance and Corrosion Resistance of AlTiCrON Multilayered Coatings on AISI M2 Tool Steel

This study utilized the reaction of O2/N2 gases and Al0.67Ti0.33/Cr (99.9%) dual targets to synthesize (Ti,Al)ON/CrON multilayered coatings on AISI M2 steel by cathodic arc deposition system. Thermal stability and corrosion resistance of the multilayered coatings for aluminum die casting applications, along with coating structure were investigated. The results showed that the structure of multilayered coatings was a B1 NaCl type. The formation of oxide phases by introducing oxygen to react with Al, Cr, and Ti elements was confirmed by XPS. The thermal stability of oxygen-doped AlTiN/CrN coatings was higher than that of one without oxygen. After the immersion tests in Al-alloy melt, the oxygen-doped AlTiN/CrN coatings deposited at the O2/N2 ratio value of 0.3 had the best improvement on the corrosion resistance among all the coated specimens.