Dissertations / Theses on the topic 'Oxynitriding'

碩士
國立臺北科技大學
材料及資源工程系研究所
98
In this study, JIS SKD11 tool steel is used and divided into three parameters of oxynitriding treatment. The first step is to change the temperature of oxynitriding treatment (470°C-8 h, 480°C-8 h, 490°C-8 h and 510°C-8 h) and keep the same post-oxidation time (30 min), then to find the optimal temperature of nitriding. The second step is change the soaking time of oxynitriding treatment (480°C-6 h, 480°C-8 h and 480°C-10 h) and soaking time of post-oxidation is same. Finally, we use the different soaking time of post-oxidation (480°C-8 h-30 min, 480°C-8 h-60 min, and 480°C-8 h-90 min) to evaluate and compare the effects of mechanical properties and microstructure on JIS SKD11 steel by different parameters of oxynitriding treatment. The experimental result showed that the hardness was increased by oxynitriding treatment after wear test. By the XRD analysis, it showed the ε phase (Fe3N) compounds were appeared on the steel surface which increased the wear resistance of material. Beside, increased the temperature of oxynitriding (470°C → 480°C → 490°C → 510°C) and kept the same soaking time of oxynitriding and post-oxidation treatment. It can be found as the temperature is increasing, the thickness of nitriding layer is higher and hardness is lower for JIS SKD11 by oxynitriding treatment. This result show that the substrate begging to soften after longer time and higher temperature reaction. In addition, by the different oxynitriding time (480°C-6 h, 480°C-8 h and 480°C-10 h) and post-oxidation of 30 min, the optimal wear-resistance was appeared in 8 hours after west test. Increasing the soaking time of post-oxidation (480°C-8 h-30min → 480°C-8 h-60min → 480°C-8 h-90min), it will affect the depth of nitriding layer. In this study, the nitriding layer was from 40 μm decreased to 10 μm that result in the lower hardness and poor wear-resistance. All these experimental results show that the optimal parameters of oxynitriding is 480°C-8 h-30 min for JIS SKD11 tool steel.

碩士
國立臺北科技大學
材料及資源工程系研究所
101
A surface treatment is usually used to improve tool life. The diamond-like carbon (DLC) film has many superior properties, such as high mechanical hardness, high wear resistance, a low friction coefficient and chemical inertness. The oxynitriding process uses air or steam at the end of the nitriding stage; used as an oxidizing medium, it is an integral part of the treatment. During the oxidation process, most steels can form several kinds of oxides (Fe2O3 and Fe3O4). Generally, the Fe3O4 layer of oxidation treatment can effectively protect and improve the erosion and corrosion resistance of steels. In addition, ASP23 is a cold work tool steel powder smelting, which provides a very high wear resistance and excellent toughness. There have been many previous experimental results that suggest that the plasma CVD using a DC-pulsed discharge could be effective in improving the adhesion and properties of coating films. Therefore, the oxynitriding/DLC duplex treatment is utilized for treated ASP23 High Speed steel in an attempt to increase the tool life. In this study, diamond-like carbon films were prepared by DC-pulsed PECVD after oxynitriding-treatment of ASP23 high speed steel. In order to investigate the DLC film properties, the Raman spectroscopy analysis, wear test, adhesion and hardness tests were performed. The chief study of the parameters of a DC-pulsed PECVD process included the coating time (60 min, 90 min and 120 min) and duty cycles (5%, 10%, 15% and 20%). The experimental results showed that a 0.06 mm oxynitride layer and 1-2 μm of DLC film could be obtained after the ASP23 high speed steel was treated by an oxynitride/DLC duplex treatment. The duplex coating layers had optimal properties when treated with a low pulse voltage (-2 kV), a coating time of 90 minutes and duty cycles kept at 10%. Meanwhile, the oxynitride/DLC duplex treatment possessed the highest surface hardness (Hv0.01 1931), and the lowest volume loss (3.46 × 10-3 mm3) after wear tests (load was 400 g). In addition, when comparing non-treated (Rp = 5442.6 Ω‧cm2) and oxynitriding (Rp = 7719.0 Ω‧cm2) specimens, the oxynitride/DLC duplex coating had the highest polarization resistance (Rp) of 11445.0 Ω‧cm2 in 3.5 wt% NaCl solution. These results were significant in indicating that the oxynitride/DLC duplex treatment possessed optimal corrosion resistance.

碩士
國立臺北科技大學
材料科學與工程研究所
105
PM30 is a cobalt alloy high performance PM high speed steel. The cobalt addition of approximate 8.5% has a positive influence on the strength, hardness, temper resistance and modulus of elasticity. As cobalt does not form carbides, the presence of cobalt has little influence on wear resistance. In order to improve the tool life and wear resistance, this research used duplex surface treatment to increase the tool life of PM30 high speed steel. Furthermore, the oxynitriding treatment can form several kinds of nitrides (Fe2N, Fe3N and Fe4N) and oxides (Fe2O3 and Fe3O4). A complex oxide layer, with Fe2O3 and Fe3O4 structures, is formed on the surface, improving the corrosion and erosion properties of the steel. Moreover, the oxynitriding layer not only improves wear resistance but also the adhesive strength as an intermediate layer. On the other hand, the amorphous hydrogenated carbon (a-C:H) coatings have attracted a great deal of attention because of their low friction, high hardness, high elastic modulus, chemical inertness, biocompatibility, and high degree of resistance to wear. In particular, the adhesion and other properties of DLC film can be effectively improved by an asymmetric bipolar-pulsed plasma CVD process; therefore, the oxynitriding/DLC duplex treatment is utilized for treating PM30 high speed steel in an attempt to increase tool life. In this study, DLC films were prepared by DC-pulsed PECVD after oxynitriding treatment of PM30 high speed steel. The experimental parameters included various CH4 gas flows (3, 7, 11, 15 and 19) and H2 gas flows (0.5, 1.0 and 1.5) with asymmetric bipolar-pulsed voltage (-15+10%). In order to compare the properties of the DLC films for oxynitriding/DLC-treated PM30 high speed steel, Raman spectroscopy analysis, wear tests, scratch tests, hardness tests, Rockwell indentation, nano-indentation and corrosion resistance inspections were performed. The experimental results show that 28 μm of oxynitriding layer could be successfully obtained after PM30 High Speed Steel was treated by the oxynitriding/DLC duplex treatment. As the CH4 gas flow increased to 19 sccm, the thermal energy which each ion gained was insufficient; this obviously resulted in poor adhesion and properties. Consequently, the duplex coating layers had optimal properties when DLC films were treated by asymmetric bipolar-pulsed voltage and with an appropriate volt (150 V). Meanwhile, the deposition time was 90 min, and the CH4 gas flow was maintained at 15 sccm, respectively. As a result, it possessed the lowest wear volume loss (when the load of 1.96 N and 4.9 N was 3.82 × 10-3 mm3 and 5.49 × 10-3 mm3, respectively). In this work, it was shown that more sp3 bond content in DLC film will improve its corrosion resistance. Indeed, when the CH4 gas flow increased to 15 sccm, it had the lowest corrosion current (Icorr = 1.43 × 10-4 A·cm-2) and highest polarization resistance (Rp = 531.94 Ω·cm2) in 3.5 wt% NaCl solutions. The study results also confirm that the optimal wear and corrosion resistance of PM30 high speed steel can be effectively improved through the asymmetric bipolar-pulsed PECVD-treated oxynitriding/DLC duplex treatment.

碩士
國立臺北科技大學
材料科學與工程研究所
99
AISI H13 tool steels are almost exclusively used on extrusion and die-casting dies. They are characterized by high strength, ductility, good tempering resistance, and moderate cost. Thermal fatigue and erosion are the most important factors limiting tool life and resulting in the tool failure of hot work tool steels. A surface treatment is usually used to increase wear resistance as well as to improve corrosion resistance. The oxynitriding process uses air or steam at the end of the nitriding stage; used as an oxidizing medium, it is an integral part of the treatment. In addition, the TiAlN coating has high strength and thermally stable properties resulting from the cathodic arc PVD treatment; therefore, the oxynitriding/TiAlN duplex is used to treat AISI H13 tool steel in an attempt to increase tool life. In this study, the specimens were subjected to various surface treatments including oxynitriding, TiAlN coating, and oxynitriding/TiAlN duplex treatments. In order to investigate the molten loss for melting A390 aluminum alloy, wear resistance and corrosion resistance for different surface treatments were examined. XRD, SEM and OM microstructural inspections, erosion, wear and corrosion tests were performed. The experimental results indicated that a 0.03-0.04 mm oxynitride layer and a 3-4μm TiAlN thin film could be obtained after the oxynitride/TiAlN complex treatment. This duplex treatment had the highest surface hardness (Hv0.01 3463); thus, the wear behavior results showed both higher hardness and a lower wear volume (0.05 mm3). Moreover, the higher hardness and high thermally stable properties of the oxynitride/TiAlN duplex layer were found to have the most effective erosion resistance. The corrosion test results also showed the duplex layer to have the optimum corrosion currents of 9.64 × 10-5 and 4.42 × 10-6 A in 0.15 M HCl and 3.5 wt% NaCl solutions, respectively, signifying that the complex treatment resulted in the best corrosion resistance.

碩士
國立臺北科技大學
材料及資源工程系研究所
100
A surface treatment is usually used to improve tool life. DLC has many superior properties, such as high mechanical hardness, high wear resistance, a low friction coefficient and chemical inertness. The oxynitriding process uses air or steam at the end of the nitriding stage as an oxidizing medium, which is an integral part of the treatment. During the oxidation process, most steels can form several kinds of oxides (Fe2O3 and Fe3O4). Generally, the Fe3O4 layer of the oxidation treatment can effectively protect and improve the erosion and corrosion resistance of steels. Therefore, the oxynitriding/DLC duplex treatment was utilized for treating AISI H13 tool steel in an attempt to increase tool life. In this study, the diamond-like carbon films were prepared by DC-pulsed plasma CVD after the oxynitride treatment of AISI H13 tool steel. In order to investigate the DLC films properties, Raman spectroscopy analysis, wear test, adhesion and hardness tests were performed. The study of the parameters of DC-pulsed plasma CVD process included the pulsed voltage, pre-treatment of argon gas and the substrate temperature. The experimental results showed that a 0.05-0.06 mm oxynitride layer and 1-2 μm of DLC thin film could be obtained after the oxynitride/DLC duplex treatment. The duplex coating layers had the optimal properties when treated by a low pulse voltage (-1.5 kV), pre-treatment of argon gas for 15 min and the substrate kept at a 50°C condition. Meanwhile, the oxynitride/DLC duplex treatments possessed the highest surface hardness (Hv0.01 1457), lowest wear volume (2.25 × 10-3 mm3) and lower friction coefficient (0.06).

碩士
國立臺北科技大學
材料科學與工程研究所
106
Vanadis 8 tool steel is a chromium-molybdenum-vanadium alloy steel usually used for cold forging, powder pressing, extruder screw, and so on. MC-type carbides are precipitated in the matrix, making Vanadis 8 harder than other steels. In order to extend the tool life and wear resistance, this research utilized a duplex surface treatment on Vanadis 8 tool steel. Generally speaking, oxynitriding (ONC) treatment consists of oxide layer and nitride layer. Among them, oxide layer with Fe2O3 and Fe3O4 structure that forms dense passive film improves the corrosion properties, while nitride layer can enhance the surface hardness. Actually, the oxynitriding layer improves not only the corrosion properties, but also the adhesive strength as an interlayer. On the other hand, diamond-like carbon (DLC) has attracted wide attention owing to its unique properties, such as low friction, chemical inertness and good wear resistance. Furthermore, since the DC-pulsed plasma CVD technique can effectively improve the properties of DLC, our research utilized the ONC/DLC duplex treatment on Vanadis 8 tool steel, in order to investigate the characteristics of DLC films, as well as to increase tool life. In this paper, DLC films were deposited via DC-pulsed plasma CVD technique, by changing the gas flow of CH4 (5, 10, 15, 20 scccm) and Ar (1, 1.5, 2, 2.5 sccm), respectively. In order to compare the properties of the DLC films for ONC/DLC treated Vanadis 8 tool steel, Raman analysis, wear tests, Rockwell indentation, nano-indentation, corrosion tests, FT-IR, water contact angle analysis and surface morphology were used to analyze the properties of DLC coatings. The experimental results showed that the oxynitriding layer was about 68 μm. In addition, DLC film could be successfully deposited on oxynitriding-treated Vanadis 8 tool steel. Since the amount of ion bombardment can cause differences in film properties, the duplex coating layers consequently had optimal properties when DLC films was treated by bipolar-pulsed voltage and with an appropriate volt (150 V). Meanwhile, the deposition time was 90 min, the gas flow of CH4 was maintained at 15 sccm, and the gas flow of Ar was at 1.5 sccm, respectively. The wear tests showed the lowest wear volume loss when the load of 2 N and 5 N was 3.81 × 10-3 mm3 and 4.01 × 10-3 mm3, respectively. Moreover, the corrosion tests also possessed the lowest corrosion current (Icorr = 4.56 × 10-5 A·cm-2) and highest polarization resistance (Rp = 1414.12 Ω·cm2) in the 3.5 wt% NaCl solutions. As the SEM surface morphology indicated, the thickness of DLC film was about 2.5 μm. According to the nano-indentation tests, the hardness of DLC film was 17.78 GPa and the elastic modulus was 191.63 GPa, respectively. Water contact angle was 78.11°, thus the DLC films could make Vanadis 8 tool steel more hydrophobic. The above analysis and test results confirmed that the duplex surface treatment can effectively improve the properties of Vanadis 8 tool steel and extend the tool life.

碩士
國立臺北科技大學
材料科學與工程研究所
102
JIS SKD11 tool steel is a commonly used cold work tool steel. Due to its high wear resistance and appropriate toughness, SKD11 is often using for stamping molds, plastic molds and other multi-function items. To improve tool life, many studies have focused on surface treatment as a method of protecting the internal material. The oxynitriding process can form several kinds of nitride (Fe2N、Fe3N and Fe4N) and oxides (Fe2O3 and Fe3O4). Generally, the Fe3O4 layer of oxidation treatment can effectively protect and improve the erosion and corrosion resistance of steels. Diamond-like carbon (DLC) films have many superior properties, such as high mechanical hardness, high wear resistance, a low friction coefficient and chemical inertness. In addition, the adhesion and properties of DLC film can be effectively improved by a DC-pulsed discharge of the plasma CVD process. Therefore, the oxynitriding/DLC duplex treatment is utilized for treated SKD11 tool steel in an attempt to increase tool life. In this study, diamond-like carbon films were prepared by DC-pulsed PECVD after oxynitriding-treatment of SKD11 tool steel. The chief study of the parameters of a DC-pulsed PECVD process included the duty cycles with unipolar negative-pulsed voltage and unbalanced bipolar-pulsed voltage. In order to evaluate the properties of the DLC films for oxynitriding/DLC-treated SKD11 tool steel, Raman spectroscopy analysis, wear tests, scratch tests, hardness tests and corrosion resistance inspections were performed. The experimental results showed that a 46 μm oxynitride layer and 1-2 μm of DLC thin film could be successfully obtained after the JIS SKD11 tool steel was treated by the oxynitriding/DLC duplex treatment. All the DLC films of the oxynitride/DLC duplex treatment possessed good adhesion and excellent characteristics. Particularly, the duplex coating layers had optimal properties when DLC films were treated by an unbalanced bipolar pulse voltage, with a low pulse voltage (-1.5 kV), a coating time of 90 min and duty cycles maintained at -15+10%. Meanwhile, the oxynitride/DLC duplex treatment possessed the highest surface hardness (Hv0.025 2830.7) and lowest wear volume loss (when the sliding speed of 0.05 m‧s-1 and load of 200 g was 4.07 × 10-3 mm3; sliding speed 0.25 m‧s-1 and load 200 g, was 4.01 × 10-3 mm3; sliding speed 0.25 m‧s-1 and load 500 g, was 5.83 × 10-3 mm3, respectively). In addition, the optimal oxynitriding/DLC duplex coating possessed the lowest corrosion current (Icorr = 2.66 × 10-6 A‧cm-2) and highest polarization resistance (Rp = 1.57 × 104 Ω‧cm2) in 3.5 wt% NaCl solutions. These results confirmed that the optimal wear and corrosion resistance followed the oxynitriding/DLC duplex treatment.

碩士
國立臺北科技大學
材料科學與工程研究所
107
PM30 high speed steel is a high-performance PM high speed steel made of a cobalt alloy. The addition of approximately 8.5% cobalt has a positive improvement on the hardness, strength, modulus of elasticity, and temper resistance. PM30 high speed steel can form many kinds of nitrides and oxides on the surface by oxynitriding (ONC) treatment. Generally speaking, nitrides are usually in the form of Fe3N and Fe4N. After oxynitriding treatment, a complex oxide layer with Fe2O3 and Fe3O4 structures is formed on the surface, thereby effectively improving the corrosion and wear resistance properties of the steel. Moreover, the oxynitriding layer not only improves the mechanical properties but also the adhesive strength as an intermediate layer. CrN and CrC films have many excellent properties, such as a low friction coefficient, high hardness, and high wear resistance and corrosion resistance. The adhesion and properties of CrN and CrC films can be obviously improved by an unbalanced magnetron sputtering process. Therefore, ONC/CrN and ONC/CrC duplex surface treatments are used for treated PM30 high speed steel in in an attempt to increase tool life. In this experiment, CrN and CrC films were deposited by unbalanced magnetron sputtering after the oxynitriding-treatment of PM30 high speed steel. Among them, the reaction gas of the CrN coating was N2. The gas flow rate was 17.5 sccm, while the reaction gas of the CrC coating was CH4 and C2H2. The gas flow rate was 3 and 6 sccm, respectively, and the coating time was maintained at 180 minutes. In order to evaluate the microstructure and properties of the CrN and CrC, hardness tests, wear tests, corrosion resistance inspections, and adhesion tests were performed. XRD, SEM, EDS and OM instruments were used to analyze the microstructure. The experimental results showed that an oxynitride layer with a thickness of about 26 μm was obtained after the PM30 high speed steel received oxynitriding treatment. The experimental results also revealed that the optimal procedure was the ONC/CrC duplex surface treatment. Meanwhile, the highest surface hardness increased to about 2852.2 HV0.1, and the adhesion was about HF3~4 level. Moreover, it possessed the lowest wear volume loss (for a sliding speed of 0.1 m•s-1 and a load of 10 N, it was 5.54 × 10-3 mm3). In addition, the optimal ONC/CrC duplex treatments also obtained the lowest corrosion current (Icorr = 5.32× 10-6 A•cm-2) and the highest polarization resistance (Rp = 1.02 × 104 Ω•cm2) in 3.5 wt% NaCl solutions. These results confirmed that the optimal corrosion resistance and wear followed the ONC/CrC duplex surface treatments.

碩士
國立臺北科技大學
材料科學與工程研究所
107
Vanadis 10 tool steel is a high vanadium alloy steel which is manufactured by powder metallurgy. The tool steel possesses great strength, hardness, and wear resistance after appropriate heat treatment, and it is generally used for various molds, cutting tools, or extruder screws. In general, oxynitriding (ONC) treatment consists of nitride (Fe3N) and oxide (Fe3O4) layers. Among them, the oxynitriding layer can improve not only the hardness but also the adhesive strength as an interlayer. Furthermore, DLC (diamond-like carbon) films have been widely applied due to their unique properties such as high strength, chemical inertness, extremely high wear resistance, and corrosion resistance. Therefore, in order to extend tool performance and life, this study employed duplex surface treatment (ONC/DLC) technique on Vanadis 10 tool steel. In this study, DLC films were coated on the oxynitriding-treated Vanadis 10 tool steel using the DC-pulsed plasma CVD technique. The different experimental parameters included the pulsed voltage (-2, -3, -4 and -5 kV) and duty cycles (9, 13, 17 and 21%). In addition, the properties of DLC films were measured by Raman spectroscopy, Rockwell indentation, wear tests, corrosion tests, water contact angle tests, four-point probes, Fourier-transform infrared spectroscopy, and surface morphology analysis, respectively. The experimental results showed that after oxynitriding treatment, the Vanadis 10 tool steel could form an oxynitriding layer with a thickness of about 68 μm. Meanwhile, the surface hardness increased to about 1293 HV0.05. Moreover, the duplex coating layers consequently had optimal properties when the DLC films were treated with an asymmetric bipolar-pulsed voltage that had the appropriate pulse frequency (10 kHz) and pulse voltage (-3 kV). Meanwhile, the duty cycle was 17%, the deposition time was 90 min, the gas flow of CH4 was maintained at 15 sccm, and the gas flow of Ar was at 1.5 sccm, respectively. The results of the Raman spectroscopy indicated that the most of the sp3 bond content in the DLC films was due to the lowest ID/IG value. The wear tests showed the lowest wear volume loss when the load of 2 N and 5 N was 3.49 × 10-3 mm3 and 4.08 × 10-3 mm3, respectively. Moreover, the optimal DLC films also possessed the lowest corrosion current density (Icorr = 7.91 × 10-5 A·cm-2) and highest polarization resistance (Rp = 1185.21 Ω·cm2) in the 3.5 wt% NaCl solution during corrosion tests. The water contact angle tests showed that the DLC films had great hydrophobicity (78.33). The FT-IR spectrum analysis found that the two strongest absorption peaks were located at 2852 cm-1 and 2921 cm-1. Overall, the study results confirmed that the duplex surface treatment (ONC/DLC) could effectively improve the properties of Vanadis 10 tool steel and extend the tool life.

碩士
國立臺北科技大學
材料科學與工程研究所
105
V4E high vanadium tool steel is a Cr-Mo-V alloy steel which possesses superior mechanical properties. It combines high wear resistance, high toughness and good stability suitable for cold work tools. On the other hand, oxynitriding treatment can form several kinds of nitrides (Fe3N and Fe4N) and oxides. A complex oxide layer, with Fe2O3 and Fe3O4 structures, is formed on the surface, improving the corrosion and erosion properties of the steel. Moreover, the oxynitriding layer not only improves wear resistance, but also adhesive strength as an intermediate layer. CrC and CrN films have many superior properties, such as high hardness and a low friction coefficient; the adhesion and properties of CrC and CrN films can be effectively improved by an unbalanced magnetron sputtering process. Therefore, the ONC/CrC and ONC/CrN duplex treatments are utilized for treated V4E high vanadium tool steel in an attempt to increase tool life. In this study, CrC and CrN films were prepared by unbalanced magnetron sputtering after oxynitriding-treatment of V4E high vanadium tool steel. The process parameters of CrC and CrN films included the target current of 2.5-3 A, pulsed frequency of 50 kHz, and coating time kept at 180 min. Among these, CrC coating has a CH4 and C2H2 gas flow of 3 and 6 seccm, respectively (substrate bias was -47 V), while the CrN coating has a N2 gas flow of 17.5 seccm (substrate bias was -85 V). In order to evaluate the properties and microstructure of the CrC and CrN, wear tests, adhesion tests, hardness tests and corrosion resistance inspections were performed. OM, XRD, SEM and EDS instruments were used to analyze the microstructure. The experimental results show that a 46 μm oxynitride layer was successfully obtained after the V4E high vanadium tool steel received an oxynitriding treatment. Thus, V4E high vanadium tool steel can be effectively strengthened by oxynitriding treatment. The test results also indicated that the optimal procedure was the ONC/CrN duplex treatment, which resulted in the highest surface hardness (2011.8 Hv0.1) with adhesion about the HF 3 level, lowest wear volume loss (for a sliding speed of 0.3 m·s-1 and a load of 9.8N, it was 2.2 × 10-3 mm3). In addition, the optimal ONC/CrN duplex coating also possessed the lowest corrosion current (Icorr = 2.22× 10-5 A·cm-2) and polarization resistance (Rp = 1.63 × 104 Ω·cm2) in 3.5 wt% NaCl solutions. These results confirmed that the optimal wear and corrosion resistance followed the ONC/CrN duplex treatment.

碩士
遠東科技大學
機械工程研究所
103
Due to its excellent mechanical properties, spheroidal graphite (SG) cast iron is often used in machinery manufacturing and car parts. In addition, nitriding and oxynitriding surface treatments can effectively improve wear and corrosion resistance on the surface of materials and have by now been widely used in surface modification for steel materials. Since SG cast iron does not contain any element that can easily form a nitride layer, it is hard to improve its surface performance either through nitriding or oxynitriding. As such, this study used electrical discharge alloying (EDA) to diffuse nitriding promoters (Ti, Cr and Al) into the surface of SG cast iron so that alloy layers respectively containing Ti, Cr and Al could be formed and subsequently subjected to either nitriding or oxynitriding. Then, these alloy layers were examined for their microstructural characteristics, hardness and corrosion resistance following nitriding or oxynitriding. Based on the results, assessment was made on the feasibility of combining EDA and nitriding in surface modification for SG cast iron. The experimental results show that the EDA alloy layers on the surface of cast iron have formed nitride or oxynitride layers on their surfaces following nitriding or oxynitriding, both of which have significantly improved the corrosion resistance and hardness of the alloy layers including those containing Ti. The experimental results show that the EDA alloy layers on the surface of cast iron have formed nitride or oxynitride layers on their surfaces following nitriding or oxynitriding, both of which have significantly improved the corrosion resistance and hardness of the alloy layers including those containing Ti. Electrochemical polarization testing reveals that the alloy layers containing Ti have the greatest corrosion resistance. Their X-ray diffraction analysis further shows that those subjected to nitriding have Fe3N as the main constituent phase while those subjected to oxynitriding have main constituent phases including Fe3O4 and FeN0.0760. Analysis of the alloy layers containing Al subjected to either nitriding or oxynitrding reveals that these alloy layers also exhibit improved corrosion resistance and hardness. Their X-ray diffraction analysis further shows that those subjected to nitriding have main constituent phases including Fe3N, Al192.40Fe46.22 and Al8Fe2Si while those subjected to oxynitriding have main constituent phases including Fe3O4 and FeN0.0760. On the other hand, the alloy layers containing Cr subjected to either ntiriding or oxynitriding have the best corrosion resistance and hardness among the three types of alloy layers. Their X-ray diffraction analysis further reveals that those subjected to nitriding have Fe3N as the main constituent phase while those subjected to oxynitriding have main constituent phases including Fe3O4 and FeN0.0897.

碩士
遠東科技大學
機械工程研究所
102
Spheroidal graphite (SG) cast iron and medium carbon steel are widely used in components such as thrust washer, rollers and forming molds. Since these components are likely to be exposed to wear, corrosion and thermal oxidation in actual use, several methods are available that can improve their strength and hardness. A common method is the plasma transferred arc overlaying process for surface modification. In this process, these wear components are overlaid with high speed steel (HSS) coatings to increase the wear resistance of SG cast iron and medium carbon steel. On the other hand, the oxynitriding process is a surface treatment method developed to improve the less than satisfactory corrosion resistance of post-nitriding surfaces. By using computer-aided control of nitrogen potential in the furnace atmosphere and the post-oxidation process, wear-, erosion- and corrosion-resistant hardened layers are generated on surfaces. To achieve this, this study proposed the combination of the two processes, oxynitriding and plasma transferred arc overlaying, for the surface modification of SG cast iron and medium carbon steel as well as the use of HSS coated alloy commonly used in wear components and forming molds. The resultant HSS coated layers after plasma transferred arc overlaying followed by oxynitriding were then subject to microstructure analysis for investigating the effects of various carbides, nitrides and oxides on the hardness of modified layers. Experiment results showed that approximately 10m thick oxynitrided layers were generated on the plasma transferred coated layers after oxynitriding. Moreover, the hardness of the original coated layers increased by HRC 65 because the oxynitriding temperature was also that for HSS tempering and the distribution of hardness in their cross-sections revealed the maximum hardness up to Hv 1400. Results of X-ray diffraction analysis showed that the main constituent phases of the original coated layers were austenite, V8C7 and M23C6 while those of the oxynitriding-treated layers were-Fe, Fe3O4 and Fe4N. Polarization testing revealed that the oxynitriding-treated layers had lower corrosion current densities in a 3.5 wt.% NaCl corrosion solution that simulated seawater and suspected passivation occurred when the corrosion potential (Ecorr.) was -0.5V, which improved the corrosion resistance of the coated layers.