Compressive behavior of Cu-Ni alloy foams: Effects of grain size, porosity, pore directionality, and chemical composition

Gubicza, Jenő,Jenei, Pé,ter,Nam, Kyungju,Ká,dá,r, Csilla,Jo, Hyungyung,Choe, Heeman Elsevier 2018 Materials science & engineering. properties, micro Vol.725 No.-

<P><B>Abstract</B></P> <P>Experiments were conducted to study the compression behavior of Cu-Ni foams prepared using freeze casting. The struts of the foam samples were solid-solutioned with differing Cu/Ni ratios, after which the grain size in the struts was measured using scanning electron microscopy. The compression performance of the samples was studied in both parallel and perpendicular directions to the temperature gradient, and compared with model calculations. It was confirmed that alloying increased the yield strength of the struts. The experimentally determined yield strength and elastic modulus were compared with model calculations, which revealed that the elastic modulus of the foams was lower than the values calculated from the classical compression and Gibson-Ashby models due to variation in the thickness of the struts. It was also found that the alloying of Cu and Ni improved the mechanical performance of the alloy foams because the absorbed energy for the alloys was considerably higher than that for the pure foams.</P>

Microstructure of ultrafine-grained fcc metals produced by severe plastic deformation

J. Gubicza,N.Q. Chinh,Gy. Kr?llics,I. Schiller,T. Ung?r 한국물리학회 2006 Current Applied Physics Vol.6 No.2

Ion implantations with energies less than 100 keV and current densities of 10151018 ions/cm2 were conducted to polymers, met-als, and diamond gemstone. Physical and chemical phenomena and mechanical properties of the implanted materials wereinvestigated.Single or mixed ions of N, He, C were implanted onto polyethylene terephtalate (PET) to see the surface hardening eects. Multi-ple ion-implantation resulted in more increase in the surface hardness than single ion implantation at the same ion energy and dose.XPS analysis showed that CN compounds were formed when both N and C ions are implanted into PET, implying that hard par-ticle formation by reactions between the implanted ions and/or between the implanted N ions and carbon in PET in addition to thecross linking may be the mechanism of this signicant increase in hardness.Ion implantation with 70 keV N ions of >5 · 1016/cm2 ness (Ra) from 0.04l m to 0.02l m. The implanted nitrogen was detected up to at least 300 nm from the surface of the stainless steelas measured with Auger electron spectroscopy. X-ray photo-electron spectroscopy analysis showed that the implanted N formedmostly Cr2N without post irradiation annealing. Hardness depth proles obtained with nano-indentation technique showed thatthe peak hardness of 14 Gpa formed at. 50 nm depth from the N ion implanted surface was about at least 2 times higher thannon-irradiated specimen.N ions were implanted into the diamond in order to change the optical band gap and then to change the emitted color. In spite ofthe restricted ion penetrated depth, uniform and vividly changed color was observed after heat treatment of the nitrogen-implanteddiamond in the vacuum or inert gas atmosphere. The changed color appeared to be black. Chemical states of the implanted nitrogen25% after N doping.. 2005 Elsevier B.V. All rights reserved.PACS:81.65.. b

Microstructure and hardness of copper-carbon nanotube composites consolidated by High Pressure Torsion

Jenei, P.,Yoon, E.Y.,Gubicza, J.,Kim, H.S.,Labar, J.L.,Ungar, T. Elsevier Sequoia 2011 Materials science & engineering. properties, micro Vol.528 No.13

Blends of Cu powders and 3vol.% carbon nanotubes (CNTs) were consolidated by High Pressure Torsion (HPT) at room temperature (RT) and 373K. The grain size, the lattice defect densities as well as the hardness of the composite samples were determined. It was found that the Cu-CNT composite processed at RT exhibited a half as large mean grain size and a three times higher dislocation density than those observed in the specimens either consolidated from pure Cu powder or processed from bulk Cu by HPT. The small grain size and the pinning effect of CNT fragments on dislocations led to significant twin boundary formation during HPT. The increase of the temperature of HPT-processing to 373K resulted in a slight increase of the grain size, and a strong decrease of the dislocation density and the twin boundary frequency in the composite. The correlation between the microstructural parameters and the flow stress calculated from the hardness was discussed.

Study of the compression and wear-resistance properties of freeze-cast Ti and Ti‒5W alloy foams for biomedical applications

Choi, Hyelim,Shil'ko, Serge,Gubicza, Jenő,Choe, Heeman Elsevier 2017 Journal of the mechanical behavior of biomedical m Vol.72 No.-

<P><B>Abstract</B></P> <P>Ti and Ti‒5wt% W alloy foams were produced by freeze-casting process and their mechanical behaviors were compared. The Ti‒5W alloy foam showed a typical acicular Widmanstätten α/β structure with most of the W dissolved in the β phase. An electron-probe microanalysis revealed that approximately 2wt% W was uniformly dissolved in the Ti matrix of Ti‒5W alloy foam with few partially dissolved W particles. The compressive-yield strength of Ti‒5W alloy foam (~323MPa) was approximately 20% higher than that of the Ti foam (~256MPa) owing to the solid-solution-strengthening effect of W in the Ti matrix, which also resulted in a dramatic improvement in the wear resistance of Ti‒5W alloy foam. The compressive behaviors of the Ti and Ti‒5W alloy foams were predicted by analytical models and compared with the experimental values. Compared with the Gibson-Ashby and cellular-lattice-structure-in-square-orientation models of porous materials, the orientation-averaging method provided prediction results that are much more accurate in terms of both the Young's modulus and the yield strength of the Ti and Ti‒5W alloy foams.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Manufacturing of Ti and Ti-W alloy foams by freeze-casting method. </LI> <LI> Compressive test of Ti and Ti-W alloy foams. </LI> <LI> Evaluation of wear resistance of Ti and Ti-W alloy foams. </LI> <LI> Analytical prediction of the Young's moduli and yield strengths of Ti and Ti-5W alloy foams. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Microstructure and Thermal Stability of Copper - Carbon Nanotube Composites Consolidated by High Pressure Torsion

Jenei, P.,Yoon, E.Y.,Gubicza, Jenő,Kim, Hyoung Seop,Lá,bá,r, J.L.,Ungá,r, Tamá,s Trans Tech Publications, Ltd. 2012 Materials science forum Vol.729 No.-

<P>Blends of Cu powders and 3 vol. % carbon nanotubes (CNTs), and an additional sample from pure Cu powder were consolidated by High Pressure Torsion (HPT) at room temperature (RT) and 373 K. The grain size, the lattice defect densities as well as the hardness of the pure and composite materials were determined. Due to the pinning effect of CNTs, the dislocation density is about three times larger, while the grain size is about half of that obtained in the sample consolidated from the pure Cu powder. The increase of the HPT-processing temperature from RT to 373 K resulted in only a slight increase of the grain size in the Cu-CNT composite while the dislocation density and the twin boundary frequency were reduced significantly. The flow stress obtained experimentally agrees well with the value calculated by the Taylor-formula indicating that the strength in both pure Cu and Cu-CNT composites is determined mainly by the interaction between dislocations. The addition of CNTs to Cu yields a significantly better thermal stability of the UFG matrix processed by HPT.</P>

Evolution of microstructure and hardness in AZ31 alloy processed by high pressure torsion

Strá,ská,, Jitka,Janeč,ek, Miloš,Gubicza, Jenő,Krajň,á,k, Tomá,š,Yoon, Eun Yoo,Kim, Hyoung Seop Elsevier 2015 Materials science & engineering. properties, micro Vol.625 No.-

<P><B>Abstract</B></P> <P>A commercial MgAlZn alloy (AZ31) was processed by high pressure torsion (HPT) at room temperature, resulting in an extreme microstructure refinement down to the grain size of 150–250nm. The microstructure evolution during HPT was investigated by transmission electron microscopy and X-ray diffraction line profile analysis. The microhardness was measured as a function of the distance from the center of the disk and the number of HPT revolutions. The detailed analysis of dislocation contrast factors in X-ray diffraction line profiles enables to determine the population of the different slip systems as a function of the imposed strain. The influence of microstructure and defect structure evolution on microhardness is discussed in detail.</P>

Microstructure and Tensile Behavior of Al7075/Al Composites Consolidated from Machining Chips Using HPT: A Way of Solid‑State Recycling

Mohammad Khajouei‑Nezhad,Mohammad Hossein Paydar,Majid Mokarizadeh Haghighi Shirazi,Jenő Gubicza 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.12

In this study the feasibility of using high-pressure torsion (HPT) process as a suitable technique for solid-state recycling ofAl alloy machining chips has been evaluated. One and four turns of HPT were used for consolidation of 7075 Al alloy chips/commercially pure Al powder mixtures at room temperature. The prepared mixtures included different weight fraction ofchips in the range from 20 to 100%. The samples were fabricated from either annealed or non-annealed chips. Additionally,the effect of the fraction of 7075 Al chips on the density, microstructure and tensile behavior of the consolidated sampleswas investigated. It was found that the addition of pure aluminum powder played an important role as a binder in the consolidationprocess and yielded improved mechanical properties due to creating lower porosity and better bonding betweenthe chips. Tensile tests revealed that the highest ultimate tensile strength and fracture strain were obtained for the compositecontaining near 50 wt% annealed 7075 Al chips, and fabricated through 4 turns of HPT. Optical microscopy investigationsdemonstrated that these conditions resulted in a fine microstructure with uniform distribution of chips.

Effect of Addition of Rare Earth Elements on the Microstructure, Texture, and Mechanical Properties of Extruded ZK60 Alloy

S. Najafi,M. Sabbaghian,A. Sheikhani,P. Nagy,K. Fekete,J. Gubicza 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.6

Microstructure, texture and mechanical properties of extruded ZK60 alloys containing different rare earth (RE) elementswere studied. Two alloys containing 1 and 2 wt% Ce-rich lanthanides as well as two other alloys with 1 and 2 wt% Y wereprepared and denoted as ZK60–1RE, ZK60–2RE, ZK60–1Y and ZK60–2Y, respectively. The results showed that the additionof RE elements refined the grain size of the ZK60 alloy, and Y had a more significant effect on the grain size reduction. The finer grain size in the ZK60–1Y and ZK60–2Y alloys (2.3 and 2.1 μm, respectively) compared to ZK60–1RE andZK60–2RE alloys (6.2 and 3.7 μm, respectively) was attributed to the pinning effect of very fine secondary phases on grainboundaries. While the ZK60–1Y alloy exhibited a fiber texture with a slight rotation of < 1010 > poles around the extrusiondirection, the ZK60–1RE alloy showed a new texture component known as RE texture. Moreover, there were no changes inthe fiber-like texture component of ZK60–2RE and ZK60–2Y alloys. The mechanical properties of the alloys were assessedby shear punch test. Accordingly, the addition of RE and Y elements enhanced the shear strength, and the maximum ultimateshear strength of 176 MPa was obtained for the ZK60–2RE alloy. The higher dislocation density, the lower volume fractionof dynamically recrystallized regions compared to other alloys, and the large fraction of secondary phase particles wereresponsible for this high strength value.

The effect of hydrogen charging on the evolution of lattice defects and phase composition during tension in 316L stainless steel

El-Tahawy, Moustafa,Um, Teakyung,Nam, Ho-Seok,Choe, Heeman,Gubicza, Jenő Elsevier 2019 Materials science & engineering. properties, micro Vol.739 No.-

<P><B>Abstract</B></P> <P>The effects of hydrogen charging on the evolution of strain-induced lattice defects and phase transformation were investigated in 316L stainless steel. The initial material was obtained by cold rolling to a thickness reduction of 20%. The surfaces of some of the initial samples were cathodically charged with hydrogen. Afterward, both the charged and uncharged samples were subjected to tension until failure. The dislocation density and twin-fault probability in the charged and uncharged specimens during tension were compared. We found that hydrogen charging reduced the degree of increase in the dislocation density and twin-fault probability during the application of tension to the same strain level. Significant martensitic phase transformation was observed in the uncharged samples tested to the strain of 10% or higher. In the hydrogen-charged samples, only a slight increase in the martensite phase fraction was detected. A correlation between the α′-martensite fraction and the dislocation density was found for the studied samples, suggesting that the lower degree of martensitic phase transformation in the charged 316L steel was caused by the smaller amount of stress developed due to the lower dislocation density. In accordance with the differences observed in the phase composition and defect densities, the hydrogen-charged material exhibited lower surface hardness.</P>

Mechanical behavior and microstructure of compressed Ti foams synthesized via freeze casting

Jenei, P.,Choi, H.,Toth, A.,Choe, H.,Gubicza, J. Elsevier 2016 Journal of the mechanical behavior of biomedical m Vol.63 No.-

Pure Ti and Ti-5%W foams were prepared via freeze casting. The porosity and grain size of both the materials were 32-33% and 15-17@?m, respectively. The mechanical behavior of the foams was investigated by uniaxial compression up to a plastic strain of ~0.26. The Young@?s moduli of both foams were ~23GPa, which was in good agreement with the value expected from their porosity. The Young@?s moduli of the foams were similar to the elastic modulus of cortical bones, thereby eliminating the osteoporosis-causing stress-shielding effect. The addition of W increased the yield strength from ~196MPa to ~235MPa. The microstructure evolution in the grains during compression was studied using electron backscatter diffraction (EBSD) and X-ray line profile analysis (XLPA). After compression up to a plastic strain of ~0.26, the average dislocation densities increased to ~3.4x10<SUP>14</SUP>m<SUP>-2</SUP> and ~5.9x10<SUP>14</SUP>m<SUP>-2</SUP> in the Ti and Ti-W foams, respectively. The higher dislocation density in the Ti-W foam can be attributed to the pinning effect of the solute tungsten atoms on dislocations. The experimentally measured yield strength was in good agreement with the strength calculated from the dislocation density and porosity. This study demonstrated that the addition of W to Ti foam is beneficial for biomedical applications, because the compressive yield strength increased while its Young@?s modulus remained similar to that of cortical bones.