Yakov Unigovski | Ben Gurion University of the Negev (original) (raw)

Papers by Yakov Unigovski

Journal of Metals, Materials and Minerals

This study examined the fatigue life (Nf) and fatigue limit (FL) of AISI 4340 steel in relation t... more This study examined the fatigue life (Nf) and fatigue limit (FL) of AISI 4340 steel in relation to surface roughness, artificial defects and shot peening. Artificial surface defects on fatigue specimens were obtained by electrical discharge machining (EDM) or by pre-corrosion in 3.5% NaCl and perchloric acid solutions, followed by a fatigue test. The presence of artificial defects of various sizes, taken into account by the area parameter, led to a significant decrease in fatigue characteristics, while shot peening contributed to their noticeable improvement. Defects resulting from electrochemical corrosion had a much greater negative effect on fatigue life than defects introduced by EDM.

Applied Surface Science, 1999

Surface and Coatings Technology, 2013

Macromolecular Symposia, 2004

Materials Science and Engineering: A, 1997

Journal of Materials Processing Technology, 2008

Journal of Light Metals, 2001

To study the fatigue life of die-cast and extruded AZ91D, AM50 and AZ31 magnesium alloys, corrosi... more To study the fatigue life of die-cast and extruded AZ91D, AM50 and AZ31 magnesium alloys, corrosion fatigue tests were carried out using a rotating beam type fatigue machine. Corrosive environment (3.5% NaCl) significantly decreases fatigue life of alloys, especially for extruded alloys. The fatigue data at high stresses were analyzed using fitting equations. Extruded alloys show a higher sensitivity to the action of NaCl solution in comparison with die-cast alloys; however, their corrosion fatigue life is longer than that of die-cast alloys. Corrosion fatigue behavior of Mg alloys correlates with their mechanochemical behavior. The latter was studied by the polarization measurements of the dissolution rate of strained alloys. TEM observations confirmed that the maximums on the curves of Mg dissolution rate dependence on the strain in NaCl solution appeared at the work-hardening stages due to the creation and destruction of dislocation pile-ups.

Journal of Applied Polymer Science, 2006

Journal of Materials Engineering and Performance, 2000

Creep and stress relaxation resistance of the most common die-cast Mg alloy AZ91D (Mg-9% Al-1% Zn... more Creep and stress relaxation resistance of the most common die-cast Mg alloy AZ91D (Mg-9% Al-1% Zn) are influenced by both casting temperature and injection rate as well as by die temperature and porosity. Relationships between viscoelastic properties of Mg alloy at 150 C and the parameters of die-casting technology are obtained and presented as simple contour plots (isograms). These properties

Materials Science Forum, 2003

It is known that electrochemical surface treatment can decrease the residual stresses and the har... more It is known that electrochemical surface treatment can decrease the residual stresses and the hardness of the surface layer as a result of the chemomechanical effect (CME), and also to improve the ability to plastic deformation, e.g., deep drawing for high strength alloys. The present research is aimed at using CME in order to improve such technological processes as rolling, deep drawing and other processes requiring an increase in the ductility of the metal surface layer using the hardness test assisted by electrochemical polarization. The hardness measurements were carried out using a microhardness tester equipped with a special three-electrode electrochemical cell on AISI 1020, 1055 and 1070 steels. The measurements were made in air and in an electrolyte, mainly, sulfuric acid solutions. It was found that the relative hardness of the steel under polarization in sulfuric acid with molarity varied from 0.5 to 2 comparing to air amounted to 20-80% with anodic current density ranged ...

Polymer Engineering and Science, 2004

ABSTRACT The morphology and stress relaxation of coextruded five-layer LLDPE (linear low-density ... more ABSTRACT The morphology and stress relaxation of coextruded five-layer LLDPE (linear low-density polyethylene)/EVA (ethylene-vinyl-acetate) copolymer films were studied. Increasing VA (vinyl acetate) content in EVA causes a decrease of shrink tension in the films, which can be explained by a decrease in amount of crystallinity. The relaxation time spectrum of the coextruded crosslinked LLDPE/EVA films is similar to the relaxation time spectrum of crosslinked LLDPE film at room temperature. However, at elevated temperatures, an additional peak appears on the spectrum of coextruded film. The cause of this peak is temperature- and stress-induced recrystallization of EVA during the relaxation test. This recrystallization was confirmed with DSC and wide angle X-ray analysis. Polym. Eng. Sci. 44:1716–1720, 2004. © 2004 Society of Plastics Engineers.

Journal of metals, materials and minerals, 2012

It is known that electrochemical surface treatment can decrease the residual stresses and the har... more It is known that electrochemical surface treatment can decrease the residual stresses and the hardness of the surface layer as a result of the chemomechanical effect (CME), and also to improve the ability to plastic deformation, e.g., deep drawing for high strength alloys. The present research is aimed at using CME in order to improve such technological processes as rolling, deep drawing and other processes requiring an increase in the ductility of the metal surface layer using the hardness test assisted by electrochemical polarization. The hardness measurements were carried out using a microhardness tester equipped with a special three-electrode electrochemical cell on AISI 1020, 1055 and 1070 steels. The measurements were made in air and in an electrolyte, mainly, sulfuric acid solutions. It was found that the relative hardness of the steel under polarization in sulfuric acid with molarity varied from 0.5 to 2 comparing to air amounted to 20-80% with anodic current density ranged ...

Light metal matrix composites (MMCs), reinforced with ceramic particles, demonstrate an improveme... more Light metal matrix composites (MMCs), reinforced with ceramic particles, demonstrate an improvement in strength, elasticity, and wear resistance with regards to matrix alloys. Unfortunately, the plasticity of MMCs is rather low, and their hardness is relatively high. Therefore, there are serious problems in formability and machinability of these materials. In the present study, an improvement in the surface plasticity of such light MMCs as Al 6063-10% SiC (AMC) and Mg AZ31-10% SiC (MgMC) as well as the high-strength Al 7075 T6 alloy under anodic polarization was observed. To assess the effect of polarization on plasticity of composites, the relative Vickers hardness (RVH) was used, which was found as the square of the ratio of the depth of penetration of the indenter into the metal in air and in the electrolyte. In the acid electrolyte 0.3 M HCl + 0.6 M NaCl, both composites demonstrated a very intense drop in RVH at low current densities (≤1 mA cm -2 ), while in tap water a small e...

It is found that the relationship between the time-to-rupture t r and the time to the onset of te... more It is found that the relationship between the time-to-rupture t r and the time to the onset of tertiary creep t οt ( t r / t ot ) in die-cast Mg-9Al alloy is equal to 1.3 and independent of stress, test temperature and diecasting parameters over the range examined. It is shown that the introduction of creep-rupture strain into Monkman-Grant relation modified by Dobes and Milicka demonstrates only the deviation range of the minimum creep rate from the average creep rate. The apparent activation energy E c of creep is below the value of magnesium self-diffusion energy ESD up to 175°C. At higher temperatures, E c > E SD , and creep deformation may be controlled by diffusion processes (dislocation climbing, etc.). The established magnitude of stress exponent n in the power law (the modified Arrhenius rate equation) within the stress range from 20 to 50 MPa is close to the value of n ≅ 3 typical of solid-solution alloys. The increase in n values at higher stresses up to ~ 5 is caused,...

Materials Science and Technology

A new technique, electrochemical cold drawing (ECD), was used to cold drawing AM60B alloy bar. Th... more A new technique, electrochemical cold drawing (ECD), was used to cold drawing AM60B alloy bar. The effects of the processing parameters on the cold drawing forces and drawn bars of magnesium alloy were investigated, including electrolyte, current density, drawing speed and drawing pass. The drawing force was significantly less than that of drawing in air due to the role of electrochemical plasticisation. This effect was greater in 0.025 M H2SO4 than it was in 0.6 M NaCl/0.3 M HCl or tap water. But it decreased in the tested electrolytes by increasing drawing speed, as well as by increasing drawing pass. To conclude, electrochemical treatment can significantly improve the metal formability and ECD is promising for forming of difficult-to-deform alloys.

Corrosion of Magnesium Alloys, 2011

Abstract: Environment-enhanced creep, which we have called ‘corrosion creep’, and high cycle corr... more Abstract: Environment-enhanced creep, which we have called ‘corrosion creep’, and high cycle corrosion fatigue were investigated in pure magnesium (Mg) and Mg alloys in different corrosive solutions in comparison to those in air. Extruded alloys, especially AZ80 and ZK60, show a significantly higher sensitivity to the action of corrosive solutions under stress in comparison with diecast alloys. The strong chemomechanical effect of increased plasticity of diecast and extruded alloys due to surface electrochemical reactions was found in borate buffer solution (pH 9.3).

Light Metal Age(USA …, 2000

EM Gutman, Y Unigovski, A Eliezer, E Abramov, L Riber Light Metal Age(USA) 58:1111, 14-16, 12/200... more EM Gutman, Y Unigovski, A Eliezer, E Abramov, L Riber Light Metal Age(USA) 58:1111, 14-16, 12/2000. Effect of die casting variables and corrosive media on impact, fatigue and creep behavior of Mg alloys was investigated. A new synergistic effect of corrosion and stress on ...

It is found that the relationship between the time-to-rupture t r and the time to the onset of te... more It is found that the relationship between the time-to-rupture t r and the time to the onset of tertiary creep t οt (t r /t ot) in die-cast Mg-9Al alloy is equal to 1.3 and independent of stress, test temperature and die-casting parameters over the range examined. It is shown that the introduction of creep-rupture strain into Monkman-Grant relation modified by Dobeš and Milička demonstrates only the deviation range of the minimum creep rate from the average creep rate. The apparent activation energy E c of creep is below the value of magnesium self-diffusion energy E SD up to 175 o C. At higher temperatures, E c > E SD , and creep deformation may be controlled by diffusion processes (dislocation climbing, etc.). The established magnitude of stress exponent n in the power law (the modified Arrhenius rate equation) within the stress range from 20 to 50 MPa is close to the value of n ≅ 3 typical of solid-solution alloys. The increase in n values at higher stresses up to ~ 5 is caused...

Journal of Metals, Materials and Minerals

This study examined the fatigue life (Nf) and fatigue limit (FL) of AISI 4340 steel in relation t... more This study examined the fatigue life (Nf) and fatigue limit (FL) of AISI 4340 steel in relation to surface roughness, artificial defects and shot peening. Artificial surface defects on fatigue specimens were obtained by electrical discharge machining (EDM) or by pre-corrosion in 3.5% NaCl and perchloric acid solutions, followed by a fatigue test. The presence of artificial defects of various sizes, taken into account by the area parameter, led to a significant decrease in fatigue characteristics, while shot peening contributed to their noticeable improvement. Defects resulting from electrochemical corrosion had a much greater negative effect on fatigue life than defects introduced by EDM.

Applied Surface Science, 1999

Surface and Coatings Technology, 2013

Macromolecular Symposia, 2004

Materials Science and Engineering: A, 1997

Journal of Materials Processing Technology, 2008

Journal of Light Metals, 2001

To study the fatigue life of die-cast and extruded AZ91D, AM50 and AZ31 magnesium alloys, corrosi... more To study the fatigue life of die-cast and extruded AZ91D, AM50 and AZ31 magnesium alloys, corrosion fatigue tests were carried out using a rotating beam type fatigue machine. Corrosive environment (3.5% NaCl) significantly decreases fatigue life of alloys, especially for extruded alloys. The fatigue data at high stresses were analyzed using fitting equations. Extruded alloys show a higher sensitivity to the action of NaCl solution in comparison with die-cast alloys; however, their corrosion fatigue life is longer than that of die-cast alloys. Corrosion fatigue behavior of Mg alloys correlates with their mechanochemical behavior. The latter was studied by the polarization measurements of the dissolution rate of strained alloys. TEM observations confirmed that the maximums on the curves of Mg dissolution rate dependence on the strain in NaCl solution appeared at the work-hardening stages due to the creation and destruction of dislocation pile-ups.

Journal of Applied Polymer Science, 2006

Journal of Materials Engineering and Performance, 2000

Creep and stress relaxation resistance of the most common die-cast Mg alloy AZ91D (Mg-9% Al-1% Zn... more Creep and stress relaxation resistance of the most common die-cast Mg alloy AZ91D (Mg-9% Al-1% Zn) are influenced by both casting temperature and injection rate as well as by die temperature and porosity. Relationships between viscoelastic properties of Mg alloy at 150 C and the parameters of die-casting technology are obtained and presented as simple contour plots (isograms). These properties

Materials Science Forum, 2003

It is known that electrochemical surface treatment can decrease the residual stresses and the har... more It is known that electrochemical surface treatment can decrease the residual stresses and the hardness of the surface layer as a result of the chemomechanical effect (CME), and also to improve the ability to plastic deformation, e.g., deep drawing for high strength alloys. The present research is aimed at using CME in order to improve such technological processes as rolling, deep drawing and other processes requiring an increase in the ductility of the metal surface layer using the hardness test assisted by electrochemical polarization. The hardness measurements were carried out using a microhardness tester equipped with a special three-electrode electrochemical cell on AISI 1020, 1055 and 1070 steels. The measurements were made in air and in an electrolyte, mainly, sulfuric acid solutions. It was found that the relative hardness of the steel under polarization in sulfuric acid with molarity varied from 0.5 to 2 comparing to air amounted to 20-80% with anodic current density ranged ...

Polymer Engineering and Science, 2004

ABSTRACT The morphology and stress relaxation of coextruded five-layer LLDPE (linear low-density ... more ABSTRACT The morphology and stress relaxation of coextruded five-layer LLDPE (linear low-density polyethylene)/EVA (ethylene-vinyl-acetate) copolymer films were studied. Increasing VA (vinyl acetate) content in EVA causes a decrease of shrink tension in the films, which can be explained by a decrease in amount of crystallinity. The relaxation time spectrum of the coextruded crosslinked LLDPE/EVA films is similar to the relaxation time spectrum of crosslinked LLDPE film at room temperature. However, at elevated temperatures, an additional peak appears on the spectrum of coextruded film. The cause of this peak is temperature- and stress-induced recrystallization of EVA during the relaxation test. This recrystallization was confirmed with DSC and wide angle X-ray analysis. Polym. Eng. Sci. 44:1716–1720, 2004. © 2004 Society of Plastics Engineers.

Journal of metals, materials and minerals, 2012

It is known that electrochemical surface treatment can decrease the residual stresses and the har... more It is known that electrochemical surface treatment can decrease the residual stresses and the hardness of the surface layer as a result of the chemomechanical effect (CME), and also to improve the ability to plastic deformation, e.g., deep drawing for high strength alloys. The present research is aimed at using CME in order to improve such technological processes as rolling, deep drawing and other processes requiring an increase in the ductility of the metal surface layer using the hardness test assisted by electrochemical polarization. The hardness measurements were carried out using a microhardness tester equipped with a special three-electrode electrochemical cell on AISI 1020, 1055 and 1070 steels. The measurements were made in air and in an electrolyte, mainly, sulfuric acid solutions. It was found that the relative hardness of the steel under polarization in sulfuric acid with molarity varied from 0.5 to 2 comparing to air amounted to 20-80% with anodic current density ranged ...

Light metal matrix composites (MMCs), reinforced with ceramic particles, demonstrate an improveme... more Light metal matrix composites (MMCs), reinforced with ceramic particles, demonstrate an improvement in strength, elasticity, and wear resistance with regards to matrix alloys. Unfortunately, the plasticity of MMCs is rather low, and their hardness is relatively high. Therefore, there are serious problems in formability and machinability of these materials. In the present study, an improvement in the surface plasticity of such light MMCs as Al 6063-10% SiC (AMC) and Mg AZ31-10% SiC (MgMC) as well as the high-strength Al 7075 T6 alloy under anodic polarization was observed. To assess the effect of polarization on plasticity of composites, the relative Vickers hardness (RVH) was used, which was found as the square of the ratio of the depth of penetration of the indenter into the metal in air and in the electrolyte. In the acid electrolyte 0.3 M HCl + 0.6 M NaCl, both composites demonstrated a very intense drop in RVH at low current densities (≤1 mA cm -2 ), while in tap water a small e...

It is found that the relationship between the time-to-rupture t r and the time to the onset of te... more It is found that the relationship between the time-to-rupture t r and the time to the onset of tertiary creep t οt ( t r / t ot ) in die-cast Mg-9Al alloy is equal to 1.3 and independent of stress, test temperature and diecasting parameters over the range examined. It is shown that the introduction of creep-rupture strain into Monkman-Grant relation modified by Dobes and Milicka demonstrates only the deviation range of the minimum creep rate from the average creep rate. The apparent activation energy E c of creep is below the value of magnesium self-diffusion energy ESD up to 175°C. At higher temperatures, E c > E SD , and creep deformation may be controlled by diffusion processes (dislocation climbing, etc.). The established magnitude of stress exponent n in the power law (the modified Arrhenius rate equation) within the stress range from 20 to 50 MPa is close to the value of n ≅ 3 typical of solid-solution alloys. The increase in n values at higher stresses up to ~ 5 is caused,...

Materials Science and Technology

A new technique, electrochemical cold drawing (ECD), was used to cold drawing AM60B alloy bar. Th... more A new technique, electrochemical cold drawing (ECD), was used to cold drawing AM60B alloy bar. The effects of the processing parameters on the cold drawing forces and drawn bars of magnesium alloy were investigated, including electrolyte, current density, drawing speed and drawing pass. The drawing force was significantly less than that of drawing in air due to the role of electrochemical plasticisation. This effect was greater in 0.025 M H2SO4 than it was in 0.6 M NaCl/0.3 M HCl or tap water. But it decreased in the tested electrolytes by increasing drawing speed, as well as by increasing drawing pass. To conclude, electrochemical treatment can significantly improve the metal formability and ECD is promising for forming of difficult-to-deform alloys.

Corrosion of Magnesium Alloys, 2011

Abstract: Environment-enhanced creep, which we have called ‘corrosion creep’, and high cycle corr... more Abstract: Environment-enhanced creep, which we have called ‘corrosion creep’, and high cycle corrosion fatigue were investigated in pure magnesium (Mg) and Mg alloys in different corrosive solutions in comparison to those in air. Extruded alloys, especially AZ80 and ZK60, show a significantly higher sensitivity to the action of corrosive solutions under stress in comparison with diecast alloys. The strong chemomechanical effect of increased plasticity of diecast and extruded alloys due to surface electrochemical reactions was found in borate buffer solution (pH 9.3).

Light Metal Age(USA …, 2000

EM Gutman, Y Unigovski, A Eliezer, E Abramov, L Riber Light Metal Age(USA) 58:1111, 14-16, 12/200... more EM Gutman, Y Unigovski, A Eliezer, E Abramov, L Riber Light Metal Age(USA) 58:1111, 14-16, 12/2000. Effect of die casting variables and corrosive media on impact, fatigue and creep behavior of Mg alloys was investigated. A new synergistic effect of corrosion and stress on ...

It is found that the relationship between the time-to-rupture t r and the time to the onset of te... more It is found that the relationship between the time-to-rupture t r and the time to the onset of tertiary creep t οt (t r /t ot) in die-cast Mg-9Al alloy is equal to 1.3 and independent of stress, test temperature and die-casting parameters over the range examined. It is shown that the introduction of creep-rupture strain into Monkman-Grant relation modified by Dobeš and Milička demonstrates only the deviation range of the minimum creep rate from the average creep rate. The apparent activation energy E c of creep is below the value of magnesium self-diffusion energy E SD up to 175 o C. At higher temperatures, E c > E SD , and creep deformation may be controlled by diffusion processes (dislocation climbing, etc.). The established magnitude of stress exponent n in the power law (the modified Arrhenius rate equation) within the stress range from 20 to 50 MPa is close to the value of n ≅ 3 typical of solid-solution alloys. The increase in n values at higher stresses up to ~ 5 is caused...