Effect of pre-oxidation treatment on the bonding strength of AZ31/carbon-fiber-reinforced plastic composites fabricated by thermal laser joining

Jeoung Han Kim(김정한),Barton Mensah Arkhurst1,Jae Bok Seol(설재복),Youn Seoung Lee(이연승),S.B. Han(한상배),Mok-Young Lee(이목영) 한국소성가공학회 2018 한국소성가공학회 학술대회 논문집 Vol.2018 No.5

Evolution of Microstructure and Mechanical Properties of Oxide Dispersion Strengthened Steels Made from Water-Atomized Ferritic Powder

Arkhurst, Barton Mensah,Kim, Jeoung Han Springer-Verlag 2018 METALS AND MATERIALS International Vol.24 No.3

<P>Nano-structured oxide dispersion strengthened (ODS) steels produced from a 410L stainless steel powder prepared by water-atomization was studied. The influences of Ti content and milling time on the microstructure and the mechanical properties were analysed. It was found that the ODS steels made from the Si bearing 410L powder contained Y-Ti-O, Y-Ti-Si-O, Y-Si-O, and TiO2 oxides. Most nanoparticles produced after 80 h of milling were aggregated nanoparticles; however, after 160 h of milling, most aggregated nanoparticles dissociated into smaller individual nanoparticles. Perfect mixing of Y and Ti was not achieved even after the longer milling time of 160 h; instead, the longer hours of milling rather resulted in Si incorporation into the Y-Ti-O rich nanoparticles and a change in the matrix morphology from an equiaxed microstructure to a tempered martensite-like microstructure. The overall micro-hardness of the ODS steel increased with the increase of milling time. After 80 and 160 h, the microhardnesses were over 400 HV, which primarily resulted from the finer dispersed nanoparticles and in part to the formation of martensitic phases. Tensile strength of the 410L ODS steels was comparable with that of ODS steel produced from gas-atomized powder.</P>

Hot metal pressing joining of carbon fiber reinforced plastic to AZ31 Mg alloy and the effect of the oxide surface layer on joint strength

Arkhurst, Barton Mensah,Kim, Jeoung Han,Lee, Mok-Young Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.477 No.-

<P><B>Abstract</B></P> <P>In this study, a new material joining process called hot metal pressing (HMP) was developed. The feasibility, nature and mechanisms of this process were investigated for joining carbon fiber reinforced plastic (CFRP) and an AZ31 Mg alloy. Two sets of joint specimens were prepared, one set with as-received Mg sheets, and the other with Mg alloy sheets that had been annealed for different duration times. It was observed that an oxide layer, introduced on the surface of the Mg alloy by the annealing, had a significant influence on the bonding strength of the joints. Tensile shear test results showed that a high strength joint of approximately 5.1kN could be achieved. Bubble formation and the decomposition of the CFRP near the joint interface was observed on the joints with the as-received Mg alloy sheets, but was not observed on the joints that had oxide layers on the Mg alloy sheets after annealing. Moreover, the oxide layer grew into the CFRP near the joint interface for joints with the annealed Mg alloy sheets, indicating the possibility of mechanical anchoring effects which greatly enhanced the joining strength.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Joining of a CFRP to an AZ31 Mg alloy was successfully achieved. </LI> <LI> Higher joint strengths were achieved by formation of an oxide layer on the surface of the AZ31 Mg alloy. </LI> <LI> Decomposition of the CFRP and significant bubble formation was prohibited by the formation of oxide layer. </LI> <LI> Oxide layer was observed to grow into the CFRP near the joint interfaces. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Direct Laser Deposition of 14Cr Oxide Dispersion Strengthened Steel Powders Using Y₂O₃ and HfO₂ Dispersoids

Barton Mensah Arkhurst,Jin-ju Park,Chang-hoon Lee,Jeoung Han Kim 대한금속재료학회(구 대한금속학회) 2017 대한금속·재료학회지 Vol.55 No.8

This study investigated the feasibility of using HfO₂ as a dispersoid in the additive manufacturing process, compared to Y₂O₃. The effect of pre-annealing treatment was investigated too. Scanning electron microscopy (SEM) analyses revealed unusually coarse deposition layers for both the HfO₂ and Y₂O₃ dispersed oxide dispersion strengthed (ODS) steels, in both the as-milled and the pre-annealed conditions. The deposited layer of the HfO₂ dispersed ODS steel had relatively coarser grains than the deposited layer of the Y₂O₃ dispersed ODS steel in both the as-milled and the pre-annealed conditions. Moreover, the SEM results also revealed the presence of nanometer sized particles in all the deposition layers of both Y₂O₃ and HfO₂ dispersed ODS steels, and their number densities were far lower than those in conventional bulk ODS steels. However, transmission electron microscopy analyses revealed that the dispersion and retention of nanoparticles within the melt were not achieved, even with HfO₂ as a dispersoid, in contrast to the results from the SEM analyses. Furthermore, the deposition layers of both the as-milled Y₂O₃ and HfO₂ ODS steels also exhibited an unusual nano-grained structure. The microhardnesses of the HfO₂ and the Y₂O₃ dispersed ODS steels in both the as-milled and the pre-annealed conditions were higher than the substrate. Furthermore, the Y₂O₃ dispersed ODS steel had a higher microhardness than the HfO₂ dispersed ODS steel in both the as-milled and the pre-annealed conditions. (Received February 8, 2017; Accepted March 27, 2017)

Effect of resin matrix on the strength of an AZ31 Mg alloy-CFRP joint made by the hot metal pressing technique

Arkhurst, Barton Mensah,Lee, Mokyoung,Kim, Jeoung Han Elsevier 2018 COMPOSITE STRUCTURES -BARKING THEN OXFORD- Vol.201 No.-

<P><B>Abstract</B></P> <P>This study investigated the effect of two types of carbon fiber reinforced plastics (CFRPs) with different matrices, on the strength of a metal alloy–plastic composite joint made by the hot metal pressing (HMP) technique. One set of experiments was carried out with a PAN-type CFRP with a thermoplastic polyurethane (TPU) matrix, and the other with a PAN-type CFRP with a polyamide 6 (PA6) matrix. Both matrices were joined with either as-received or annealed AZ31 Mg-alloy sheets processed at different annealing durations to produce oxide layers on the alloy sheets. Due to the complete suppression of CFRP-resin decomposition at its joint interface, the CFRP with a PA6 matrix exhibited superior joint strength as compared to the TPU-matrix CFRP, which showed partial suppression of the CFRP-resin decomposition and bubble formation, with complete suppression characterized by microcracking at its joint interface. A reaction between C and MgO was observed at the joint interface for the TPU-CFRP but not for the PA6-CFRP. The melting/decomposition temperature of the matrix materials and the influence of the oxide layer on the conduction of heat between the materials were the key determinants of the AZ Mg alloy-CFRP joint strength.</P>

Direct Laser Deposition of 14Cr Oxide Dispersion Strengthened Steel Powders Using Y2O3 and HfO2 Dispersoids

Barton Mensah Arkhurst,박진주,이창훈,김정한 대한금속·재료학회 2017 대한금속·재료학회지 Vol.55 No.8

This study investigated the feasibility of using HfO2 as a dispersoid in the additive manufacturing process, compared to Y2O3. The effect of pre-annealing treatment was investigated too. Scanning electron microscopy (SEM) analyses revealed unusually coarse deposition layers for both the HfO2 and Y2O3 dispersed oxide dispersion strengthed (ODS) steels, in both the as-milled and the pre-annealed conditions. The deposited layer of the HfO2 dispersed ODS steel had relatively coarser grains than the deposited layer of the Y2O3 dispersed ODS steel in both the as-milled and the pre-annealed conditions. Moreover, the SEM results also revealed the presence of nanometer sized particles in all the deposition layers of both Y2O3 and HfO2 dispersed ODS steels, and their number densities were far lower than those in conventional bulk ODS steels. However, transmission electron microscopy analyses revealed that the dispersion and retention of nanoparticles within the melt were not achieved, even with HfO2 as a dispersoid, in contrast to the results from the SEM analyses. Furthermore, the deposition layers of both the as-milled Y2O3 and HfO2 ODS steels also exhibited an unusual nano-grained structure. The microhardnesses of the HfO2 and the Y2O3 dispersed ODS steels in both the as-milled and the pre-annealed conditions were higher than the substrate. Furthermore, the Y2O3 dispersed ODS steel had a higher microhardness than the HfO2 dispersed ODS steel in both the as-milled and the pre-annealed conditions.

Stability of Y-Ti-O Nanoparticles During Laser Deposition of Oxide Dispersion Strengthened Steel Powder

어광준,Barton Arkhurst,김일현,김현길,김정한 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.6

This study investigated the feasibility of a direct energy deposition process for fabrication of oxide dispersionstrengthened steel cladding. The effect of the laser working power and scan speed on the microstructural stabilityof oxide nanoparticles in the deposition layer was examined. Y-Ti-O type oxide nanoparticles with a mean diameterof 45 nm were successfully dispersed by the laser deposition process. The laser working power significantlyaffected nanoparticle size and number density. A high laser power with a low scan speed seriously induced particlecoarsening and agglomeration. Compared with bulk oxide dispersion strengthened steel, the hardness of the laserdeposition layer was much lower because of a relatively coarse particle and grain size. Formation mechanism ofnanoparticles during laser deposition was discussed.