Effects of Laser Cladding for Repairing and Improving Wear of Rails

서정원,Jae–Chul Kim,권석진,전현규 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.7

Laser cladding has been applied to reduce the wear on rails in a curved track. It is important to evaluate the wear and rolling contact fatigue (RCF) characteristics of laser cladding rails. This paper evaluated the wear characteristics of three types of laser cladding, i.e., Stellite 21, Inconel 625, and Hastelloy-C. The wear of Stellite 21 was reduced by 83% as compared to the untreated rail specimen, while those of Inconel 625 and Hastelloy C were decreased by 42% and 29%, respectively. Meanwhile, when laser cladding is applied, a cladding boundary between the rail and the laser cladding is created. The cladding boundary consists of the rail base material, the heat-affected zone, and laser cladding. At the cladding boundary, various types of microstructures are distributed, and as a result the hardness changes. The wear and RCF characteristics of the cladding boundary caused by rolling contact loads have been evaluated through twin-disc tests. Since Stellite 21 has low hardness at the cladding boundary, it suffered the most severe wear and damages in three types of laser cladding. If laser cladding is applied to reduce the wear of the curved track, the damage of the boundary, as opposed to the wear characteristics, should be taken into consideration. In this paper, Stellite 21 exhibits the best wear characteristics, but Hastelloy C is found to be the most appropriate when simultaneously considering both the wear and RCF of the cladding boundary.

다층 레이저 클래딩된 과공정 Al-Si 합금의 미세조직과 내마모 특성

이형근 대한용접·접합학회 2022 대한용접·접합학회지 Vol.40 No.1

In this study, a multilayer laser-cladding method was used to increase the Si content in a hypereutectic Al-Si alloy laser cladding. One-, two-, and three-layer claddings were produced by printing Si powder paste on A1050 alumi- num surfaces using 180-, 210-, and 250-㎛-thick plastic tape, respectively, and then irradiating laser pulses over them. The two- and three-layer claddings were produced by printing on the one- and two-layer cladding surfaces, respectively. The one-layer cladding had a thickness of approximately 190 ㎛ and was uniform and defectless. The cladding had a chemical composition of Al-20.2 wt.% Si and had a fine eutectic Al-Si microstructure in most regions. By contrast, the two-layer cladding had a thickness of approximately 250 ㎛ and exhibited many pores and some cracks. The cladding had a chemical composition of Al-60.5 wt.% Si and a hypereutectic Al-Si microstructure with many coarse primary Si particles. Finally, the three-layer cladding had a thickness of approximately 280 ㎛ and exhibited many large pores and a few large cracks. The cladding had a chemical composition of Al-72.6 wt.% Si and a hypereutectic Al-Si microstructure with very coarse primary Si particles. Block-on-roll wear tests were then per- formed on the claddings. The weight losses in the one-, two-, and three-layer claddings following the wear test were 5.5, 7.7, and 8.3 mg, respectively.

Development and validation of a numerical model for steel roof cladding subject to static uplift loads

Amy C. Lovisa,Vincent Z. Wang,David J. Henderson,John D. Ginger 한국풍공학회 2013 Wind and Structures, An International Journal (WAS Vol.17 No.5

Thin, high-strength steel roof cladding is widely used in residential and industrial low-rise buildings and is susceptible to failure during severe wind storms such as cyclones. Current cladding design is heavily reliant on experimental testing for the determination of roof cladding performance. Further study is necessary to evolve current design standards, and numerical modelling of roof cladding can provide an efficient and cost effective means of studying the response of cladding in great detail. This paper details the development of a numerical model that can simulate the static response of corrugated roof cladding. Finite element analysis (FEA) was utilised to determine the response of corrugated cladding subject to a static wind pressure, which included the anisotropic material properties and strain-hardening characteristics of the thin steel roof cladding. The model was then validated by comparing the numerical data with corresponding experimental test results. Based on this comparison, the model was found to successfully predict the fastener reaction, deflection and the characteristics in deformed shape of the cladding. The validated numerical model was then used to predict the response of the cladding subject to a design cyclone pressure trace, excluding fatigue effects, to demonstrate the potential of the model to investigate more complicated loading circumstances.

Development and validation of a numerical model for steel roof cladding subject to static uplift loads

Lovisa, Amy C.,Wang, Vincent Z.,Henderson, David J.,Ginger, John D. Techno-Press 2013 Wind and Structures, An International Journal (WAS Vol.17 No.5

Thin, high-strength steel roof cladding is widely used in residential and industrial low-rise buildings and is susceptible to failure during severe wind storms such as cyclones. Current cladding design is heavily reliant on experimental testing for the determination of roof cladding performance. Further study is necessary to evolve current design standards, and numerical modelling of roof cladding can provide an efficient and cost effective means of studying the response of cladding in great detail. This paper details the development of a numerical model that can simulate the static response of corrugated roof cladding. Finite element analysis (FEA) was utilised to determine the response of corrugated cladding subject to a static wind pressure, which included the anisotropic material properties and strain-hardening characteristics of the thin steel roof cladding. The model was then validated by comparing the numerical data with corresponding experimental test results. Based on this comparison, the model was found to successfully predict the fastener reaction, deflection and the characteristics in deformed shape of the cladding. The validated numerical model was then used to predict the response of the cladding subject to a design cyclone pressure trace, excluding fatigue effects, to demonstrate the potential of the model to investigate more complicated loading circumstances.

The Circumferential Tensile Properties of Zirconium Alloy Fuel Claddings under a Simulated High Burn-Up Environment

이명호,김준환,박상윤,최병권,정용환 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.4

To study the circumferential tensile properties of fuel claddings under a simulated high burn-up environment, ring tensile tests were carried out at both room temperature and 350 °C for Zr-Nb based fuel claddings such as Zr-Nb based HANA-6 (Zr-1.10Nb-0.05Cu), HANA-4 (Zr-1.50Nb-0.40Sn-0.20Fe-0.10Cr) and Zircaloy-4 (Zr- 1.26Sn-0.23Fe-0.12Cr) cladding after they had been differently charged with hydrogen up to 2,850 ppm. The results showed that the HANA-6 cladding maintained more than a 20% circumferential elongation at room temperature without a decrease in its maximum strength when it was charged with hydrogen up to about 1,500 ppm, although the maximum circumferential strength and elongation of the Zircaloy-4 cladding decreased with increasing hydrogen content above 500 ppm. The circumferential elongation of the above claddings decreased as the hydrogen content increased at both room temperature and 350 °C but the strength increased a little with the hydrogen content at 350 °C. The maximum circumferential strength of the HANA-4 cladding also increased with the hydrogen content up to a level of 1,109 ppm, even at room temperature. It seemed that the Nb in the matrix contributed to better circumferential elongation and resistance to hydrogen embrittlement in the Zr-Nb based HANA-4 and HANA-6 claddings than was present in the Zircaloy-4 cladding. To study the circumferential tensile properties of fuel claddings under a simulated high burn-up environment, ring tensile tests were carried out at both room temperature and 350 °C for Zr-Nb based fuel claddings such as Zr-Nb based HANA-6 (Zr-1.10Nb-0.05Cu), HANA-4 (Zr-1.50Nb-0.40Sn-0.20Fe-0.10Cr) and Zircaloy-4 (Zr- 1.26Sn-0.23Fe-0.12Cr) cladding after they had been differently charged with hydrogen up to 2,850 ppm. The results showed that the HANA-6 cladding maintained more than a 20% circumferential elongation at room temperature without a decrease in its maximum strength when it was charged with hydrogen up to about 1,500 ppm, although the maximum circumferential strength and elongation of the Zircaloy-4 cladding decreased with increasing hydrogen content above 500 ppm. The circumferential elongation of the above claddings decreased as the hydrogen content increased at both room temperature and 350 °C but the strength increased a little with the hydrogen content at 350 °C. The maximum circumferential strength of the HANA-4 cladding also increased with the hydrogen content up to a level of 1,109 ppm, even at room temperature. It seemed that the Nb in the matrix contributed to better circumferential elongation and resistance to hydrogen embrittlement in the Zr-Nb based HANA-4 and HANA-6 claddings than was present in the Zircaloy-4 cladding.

레이저 클래딩 표면에 대한 젖음 특성에 관한 연구

장무연(Mu-Yeon Jang),박영환(Young-Whan Park),김태완(Tae-Wan Kim) 한국기계가공학회 2019 한국기계가공학회지 Vol.18 No.11

Laser processing has been used in various fields. In this study, the feasibility of a hydrophobic surface was investigated through the laser cladding technique. A diode laser was used, and the output was set to 600 –800 W. Seven different specimens were prepared with different cladding widths and spacings, and the contact angles for water droplets were evaluated. As a result, the contact angle of water droplets measured in the direction parallel to the cladding line was higher than that in the vertical direction. The wider the cladding width and the cladding space, the higher the contact angle in the parallel direction. It is thought that when a higher contact angle is formed in the parallel direction, more air can be placed in the valley between the cladding lines. In addition, for the hydrophobic coating effect, the contact angle of the coated cladding surface was increased by about 5–15° as a whole compared to the coated smooth surface. It was confirmed that the wetting characteristics were improved through the cladding.

Residual stress and crack initiation in laser clad composite layer with Co-based alloy and WC+NiCr

Lee, Changmin,Park, Hyungkwon,Yoo, Jaehong,Lee, Changhee,Woo, WanChuck,Park, Sunhong Elsevier 2015 APPLIED SURFACE SCIENCE - Vol.345 No.-

<P><B>Abstract</B></P> <P>Although laser cladding process has been widely used to improve the wear and corrosion resistance, there are unwanted cracking issues during and/or after laser cladding. This study investigates the tendency of Co-based WC+NiCr composite layers to cracking during the laser cladding process. Residual stress distributions of the specimen are measured using neutron diffraction and elucidate the correlation between the residual stress and the cracking in three types of cylindrical specimens; (i) no cladding substrate only, (ii) cladding with 100% stellite#6, and (iii) cladding with 55% stellite#6 and 45% technolase40s. The microstructure of the clad layer was composed of Co-based dendrite and brittle eutectic phases at the dendritic boundaries. And WC particles were distributed on the matrix forming intermediate composition region by partial melting of the surface of particles. The overlaid specimen exhibited tensile residual stress, which was accumulated through the beads due to contraction of the coating layer generated by rapid solidification, while the non-clad specimen showed compressive. Also, the specimen overlaid with 55wt% stellite#6 and 45wt% technolase40s showed a tensile stress higher than the specimen overlaid with 100% stellite#6 possibly, due to the difference between thermal expansion coefficients of the matrix and WC particles. Such tensile stresses can be potential driving force to provide an easy crack path ways for large brittle fractures combined with the crack initiation sites such as the fractured WC particles, pores and solidification cracks. WC particles directly caused clad cracks by particle fracture under the tensile stress. The pores and solidification cracks also affected as initiation sites and provided an easy crack path ways for large brittle fractures.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Major problem, clad cracking in laser cladding process, was researched. </LI> <LI> Residual stress measurements were performed quantitatively by neutron diffraction method along the surface of specimens. </LI> <LI> Relationship between the residual stress and crack initiation was showed clearly. </LI> <LI> Ceramic particle effect in the metal matrix was showed from the results of residual stress measurements. </LI> <LI> Initiation sites of generating clad cracks were specifically studied in MMC coatings. </LI> </UL> </P>

IN-PILE PERFORMANCE OF HANA CLADDING TESTED IN HALDEN REACTOR

Kim, Hyun-Gil,Park, Jeong-Yong,Jeong, Yong-Hwan,Koo, Yang-Hyun,Yoo, Jong-Sung,Mok, Yong-Kyoon,Kim, Yoon-Ho,Suh, Jung-Min Korean Nuclear Society 2014 Nuclear Engineering and Technology Vol.46 No.3

An in-pile performance test of HANA claddings was conducted at up to 67 GWD/MTU in the Halden research reactor in Norway over a 6.5 year period. Four types of HANA claddings (HANA-3, HANA-4, HANA-5, and HANA-6) and a reference Zircaloy-4 cladding were used for the in-pile test. The evaluation parameters of the HANA claddings were the corrosion behavior, dimensional changes, hydrogen uptake, and tensile strength after the claddings were tested under the simulated operation conditions of a Korean commercial reactor. The oxide thickness ranged from 15 to 37 mm at a high flux region in the test rods, and all HANA claddings showed corrosion resistance superior to the Zircaloy-4 cladding. The creep-down rate of all HANA claddings was lower than that of the Zircaloy-4 cladding. In addition, the hydrogen content of the HANA claddings ranged from 54 to 96 wppm at the high heat flux region of the test rods, whereas the hydrogen content of the Zircaloy-4 cladding was 119 wppm. The tensile strength of the HANA and Zircaloy-4 claddings was similarly increased when compared to the un-irradiated claddings owing to the radiation-induced hardening.

Comparative Study of Dry Storage Condition Characteristics of HANA and Commercial Cladding

Yongsik Yang,Jaeyong Kim,Jongdae Hong,Jangsoo Oh,Juyeop Park 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2

In nuclear fuel development research, consideration of the back-end cycle is essential. In particular, a review of an in-reactor performance of nuclear fuel related to the various degradation phenomena that can occur during spent fuel dry storage is an important area. The important factors affecting the degradation of zirconium-based cladding during dry storage are the cladding’s hydrogen concentration and rod internal pressure after irradiation. In this study, a preliminary analysis of the in-reactor behavior of the HANA cladding, which has been developed and is currently undergoing licensing review, was performed, and based on this result, a comparative analysis between nuclear fuel with HANA cladding and current commercial fuel under storage conditions was performed. The results show that the rod internal pressure of nuclear fuel with HANA cladding is not significantly different from that of commercial cladding, and the hydrogen concentration in the cladding tends to reduce due to the increased corrosion resistance, so fuel integrity in a dry storage conditions is not expected to be a major problem. Although the lack of cladding creep data under dry storage conditions, the results from the Halden research reactor test comparing in-reactor creep behavior with Zircaloy-4 showed that there is sufficient margin for degradation due to creep during storage.

In-pile Performance of HANA Cladding Tested in Halden Reactor

김현길,박정용,정용환,구양현,유종성,목용균,김윤호,서정민 한국원자력학회 2014 Nuclear Engineering and Technology Vol.46 No.3

An in-pile performance test of HANA claddings was conducted at up to 67 GWD/MTU in the Halden research reactor inNorway over a 6.5 year period. Four types of HANA claddings (HANA-3, HANA-4, HANA-5, and HANA-6) and a referenceZircaloy-4 cladding were used for the in-pile test. The evaluation parameters of the HANA claddings were the corrosionbehavior, dimensional changes, hydrogen uptake, and tensile strength after the claddings were tested under the simulatedoperation conditions of a Korean commercial reactor. The oxide thickness ranged from 15 to 37 mm at a high flux region inthe test rods, and all HANA claddings showed corrosion resistance superior to the Zircaloy-4 cladding. The creep-down rate ofall HANA claddings was lower than that of the Zircaloy-4 cladding. In addition, the hydrogen content of the HANA claddingsranged from 54 to 96 wppm at the high heat flux region of the test rods, whereas the hydrogen content of the Zircaloy-4cladding was 119 wppm. The tensile strength of the HANA and Zircaloy-4 claddings was similarly increased when comparedto the un-irradiated claddings owing to the radiation-induced hardening.