Jozef Zrnik

• professor
• COMTES FHT

Severe plastic deformation methods preserve dimensions of the material and reduce the grain size down to submicrometers. Twin-roll cast strips prepared from AA 3003 aluminum alloy (in wt.%) with 1 % Mn, 0.2 % Fe, 0.5 % Fe, 0.2 % Cu and small additions of zirconium (0.2 %) and chromium (0.1 %) were subjected to deformation by Constrained Groove Pres...

This research study has an aim to evaluate and investigate the effect of various rejuvenation heat treatments on microstructure of long-term serviced cast nickel base superalloy grade GTD-111 used as turbine blade material. The evaluated reheat treatment programs consist of solution treatment at 1195°C for 2, 3, 4 and 5 hours then following with pr...

In this work twin-roll cast AZ31 magnesium strip of thickness 5.6 mm was subjected to the heat treatment and further constrained groove pressing. A comparison of the microstructure and microhardness of as-cast, constrained groove pressed and annealed material was carried out. The twin-roll cast strip exhibits an inhomogeneous structure which is rep...

Microstructure investigation and microhardness mapping were done on the material with ultra-fine grained structure prepared by constrained groove pressing of twin-roll cast AZ31 magnesium strips. The microstructure observations showed significant drop of the grain size from 200 gm to 20 gm after constrained groove pressing. Moreover, the heterogene...

In this study, the relationship between the structure and properties of commercial purityaluminium (AW-1199) was investigated by applying constrained groove pressing (CGP) method.The refinement of the coarse grain aluminium microstructure to submicrocrystalline size by largeplastic strain at room temperature defined. The impact of various strains u...

The paper presents results of in-situ neutron diffraction experiments aimed on monitoring the phase evolution and load distribution in transformation induced plasticity (TRIP) steel when subjected to tensile loading. Tensile deformation behaviour of two TRIP-assisted multiphase steel with slightly different microstructures resulted from different t...

The work presents the results on grains refinement of steel containing 0,45 wt pct carbon resulted from severe plastic deformation (SPD). Different steel structures from prior solutioning and/or thermomechanical treatment were prepared for deformation experimental. A coarse grain ferrite-pearlite structure was achieved applying solutioning. By appl...

The paper presents results of in-situ neutron diffraction experiments aimed on monitoring the phase evolution and load distribution in TRIP steel when subjected to tensile loading. Tensile deformation behaviour of TRIP steel with different initial microstructures showed that the applied tensile load is redistributed at the yield point and the harde...

High strength and ductility of the TRIP (Transformation Induced Plasticity) steels is attributed to the transformation induced plasticity effect resulting from the strain induced martensitic transformation of the retained austenite in the multiphase (ferrite, bainite) microstructure. The precise characterisation of the multiple microstructure of lo...

The work presents the results on grains refinement of steel containing 0,45 wt pct carbon resulted from severe plastic deformation (SPD). Different steel structures from prior solutioning and/or thermomechanical treatment were prepared for deformation experimental. A coarse grain ferrite-pearlite structure was achieved applying solutioning. By appl...

The present work deals with grain refinement of medium carbon steel AISI 1045 (0.45 wt.% C) having different initial ferrite-pearlite microstructure resulted from thermal and thermomechanical (TM) treatment. The purpose of prior TM steel processing was to refine grains of ferrite phase and to modify coarse lamellae pearlite structure. The final gra...

Conventional soft annealing of steel is normally carried out in continuous and batch furnaces with annealing times of up to several tens of hours. The typical annealing temperature is just below the transformation temperature AC1, but the soaking times are varied. The hold is followed by slow cooling to room temperature. During annealing, recovery...

In this study ultrafine grain structure evolution during high pressure torsion (HPT) of commercial aluminium alloy AA6082 at increased temperature is presented. Two different initial structural states of the alloy were prepared by thermal treatment. The progress in structure refinement in dependence on the shear strain level strain was investigated...

In this study, ultrafine grain structure evolution during high pressure torsion (HPT) of commercial aluminium alloy AA6082 at an elevated temperature is presented. Two different initial structural states of the alloy were prepared by thermal treatment. The dependence of the progress of microstructure refinement on shear strain was investigated by T...

The creep degraded nickel base single crystal superalloy CMSX-4 of two axial orientations [001]and [111] was investigated with aim to assess the structure degradation. Constant load creep tests were conducted in the stress/temperature ranges of 250-780 MPa/750-950°C resulting in rupture time variation from 50 to 4000 hours. A combination of scannin...

An important measure in steel processing industry is achieving the required mechanical properties and micro structure of the material. A new phenomenon has been discovered recently which allows to refine ferrite grain significantly and to spheroidise carbides over a very short time compared to conventional heat treatment techniques. The newly devel...

This paper provides information of the uniform grain structure after application of hot and cold rolling conditions and recrystallization processes followed by various annealing times in NiMoCr alloy. The different structure would result in high temperature mechanical properties such as yield strength, tensile strength, ductility, fatigue, and cree...

The objective of this research is to investigate the most appropriate heat treatment condition for a nickel base superalloy GTD-111 turbine blade with the suitable microstructure to enable the phase stability after long-term thermal exposure. The received turbine blade that had been used under load and high temperature showed the coarse gamma prime...

Creep behaviour of nickel-base solid solution strengthened NiMoCr alloy after different applied hot and cold rolling conditions was investigated, The results of creep tests showed that the creep characteristics including strain rate, fracture strain, and lifetime were greatly dependent on the plastic deformation conditions carried out prior to the...

The paper presents results of in-situ neutron diffraction experiments aimed on monitoring the phase evolution and load distribution in TRIP steel when subjected to tensile loading. Tensile deformation behaviour of TRIP steel with different initial microstructures showed that the applied tensile load is redistributed at the yield point and the harde...

The importance of bearing steels in industrial production is continuously increasing. These steels are not fit for working unless soft- Annealed. The purpose of this annealing process is to obtain globular carbides which will be uniformly distributed in the matrix. Conventional methods of annealing steel stock to obtain globular pearlite require lo...

The present research was focused on improving mechanical properties of the structural carbon steel AISI 1042. The microstructure of this material can be transformed by Accelerated Carbide Spheroidisation and Refinement (ASR) process. It increases the proof stress and ultimate tensile strength and, at the same time, the plasticity and toughness. A r...

In this study ultrafine grain structure evolution during high pressure torsion (HPT) of commercial aluminium alloy AA6082 at increased temperature is presented. Two different initial structural states of the alloy were prepared by thermal treatment. The progress in structure refinement in dependence on the shear strain level strain was investigated...

L'elevata resistenza meccanica e duttilità degli acciai TRIP (Transformation-Induced Plasticity) sono dovute fondamentalmente grazie alla trasformazione dell'austenite residua in martensite durante la deformazione, nella struttura multi-fasica (ferritico bainitica). L'effetto dei parametri di processo, durante i trattamenti termomeccanici (TMP) su...

Main changes which appear in microstructure of Ni base superalloys during creep exposure is the directional coarsening (rafting) of originally cubic γ' precipitates embedded in γ matrix. The progress in γ' degradation can be assessed with help of the analysis of geometrical parameters of the γ' microstructure. Determination of the morphological cha...

Grain refinement upon the severe plastic deformation (SPD) at low temperatures (below the recrystallization temperature) and an unusual improvement the properties of such materials are shown reliably. However, the industrial application is limited due to the absence of effective continuous SPD processes. The potential of development of continuous S...

Upon the ECA pressing at 400°C of the AISI 1045 steel with 0.45% C, the processes of dynamic recovery are developed with the formation of subgrains of ~320 nm in size and isolated grains of submicron size with high-angle boundaries. The fragmentation and partial spheroidization of the cementite lamellae is observed within the pearlite colonies. Def...

Methods of severe plastic deformation of ductile metals and alloys offer the possibility of processing engineering materials to very high strength with good ductility. After typical amount of processing strain a material with submicron grain size is obtained with boundaries of rather low misorientation angles and grains containing a high density of...

The structure and properties of the 0,09% C-Mn-Si-Nb-V-Ti, 0,1% C-Mn-V-Ti and 0,09% C-Mo-V-Nb low-carbon steels were studied after cold equal-channel angular pressing (ECAP). ECAP leads to the formation of partially submicrocrystalline structure with a grain size of 150 – 300 nm. The submicrocrystalline 0,09% C-Mn-Si-Nb-V-Ti steel compared with the...

The severe plastic deformation method known as constrained groove pressing was used to produce ultrafine-grained microstructure in recrystallized aluminium (99.99%) at room temperature. The impact of repeated groove pressing, upon microstructure refinement was investigated by transmission electron microscopy of thin foils. Changes in mechanical pro...

The severe plastic deformation method known as constrained groove pressing (CGP) was used to produce ultrafine grained (UFG) structure in recrystallized aluminium (99.99%) at room temperature. The impact of repeated groove pressing, upon microstructure refinement was investigated by transmission electron microscopy (TEM) of thin foils. The changes...

The article focuses on the severe plastic deformation (SPD) of low carbon (LC) steel AISI 1010 (ČSN 12014) performed at increased temperature. The grain refinement of ferrite structure is monitored and described with respect to different initial structure of steel modified by thermomechanical (TM) treatment prior severe plastic deformation. The ref...

Tensile deformation behavior of two transformation-induced plasticity (TRIP)–assisted multiphase steels with slightly different microstructures due to different thermomechanical treatment conditions applied was investigated by in-situ neutron diffraction. The steel with lower austenite volume fraction (f γ =0.04) and higher volume fraction of need...

The deformation behaviour of two transformation induced plasticity (TRIP)-assisted steels with slightly different microstructures due to different thermo-mechanically controlled processing (TMCP) was investigated by the in situ neutron diffraction technique during tensile straining at room temperature and two elevated (50 and 100 °C) temperatures....

The structure and properties of 0,14% C and 0,1% C - B low-carbon steels taken in two initial states, martensitic and ferritic-pearlitic, were studied after cold equal-channel angular (ECA) pressing. ECA pressing leads to the formation of only partially submicrocrystalline structure with a grain size of 150 – 300 nm, depending on the steel alloying...

SPD methods are used to convert coarse grain metals and alloys into ultrafine grained (UFG) materials. Obtained UFG materials then possess improved mechanical and physical properties which destine them for a wide commercial use. This paper, in one direction, looks into historical development of SPD processes and their effect at obtaining fine cryst...

In order to assess the material degradation of exposed gas turbine high temperature components, the creep degraded CMSX-4 single-crystal nickel-base superalloy with two axial orientations [001] and [111] was investigated. Constant load creep tests were conducted in the stress/temperature ranges of 250–780 MPa/750–950 °C resulting in rupture time va...

In the present work, the development of finite element (FE) models to simulate the nanoindentation processes in various TiB2-based nanostructured coatings was investigated. The developed nanoindentation FE models were able to simulate the indentation loading-unloading curves of the coating/substrate system. The model could also be used to extract t...

Commercial low carbon steel AISI 1010 was subjected to Equal Angular Channel Pressing (ECAP) at different temperatures. The paper describes the refinement of the coarse grained ferrite microstructure to submicrocrystalline range by large plastic strain. The steel was deformed in an ECAP tool with a channel angle φ = 90°, at different temperature in...

This research provides an attempt to achieve uniform grain structure by recrystallization process in NiMoCr alloy after different hot- and cold-working application. The changes in microstructure resulting from thermomechanical processing were investigated by optical microscopy. The results showed that homogeneity of the recrystallized structure is...

The main emphasis of this study has been placed on thermomechanical processing simulations performed using press forging. In order to develop a comprehensive understanding of the effect of large deformation of bulk specimens, introduced in the austenite recrystallized, nonrecrystallized and intercritical temperature regions, on the microstructure e...

The thermomechanical processing of NiMoCr solid solution nickel base superalloy is the way to considerably influence the grain size. As uniform coarse grain size increases the creep strength and crack growth resistance. In the work, the processing to achieve uniform recrystallized grain structure with variation of thermomechanical parameters is inv...

The Udimet 500 nickel base superalloy blade exposed for 50000 hours in land base gas turbine working conditions faced the structure degradation. Six different heat treatments procedures have been applied (the blades were exposed at 900 °C and 1000 °C for different periods with maximum hold of 2500 hours) to rejuvenate the degraded structure. Metall...

Low carbon steel AISI 10 was subjected to a severe plastic deformation technique called Equal Angular Channel Pressing (ECAP) at different increased temperatures. The steel was subjected to ECAP with channel’s angle j = 90°, at different temperature in range of 150 - 300 °C. The number of passes at each temperature was N = 3. Light, scanning electr...

In situ neutron diffraction experiment was employed for monitoring of conditioned austenite transformation to ferrite, and also for the retained austenite stability evaluation during subsequent mechanical loading. The progress in the austenite decomposition to ferrite is monitored at different transformation temperatures. The relevant information o...

Microstructure of Waspaloy and DT750 Ni-base superalloys was investigated after the heat treatment as well as after long thermal exposure by Small-Angle Neutron Scattering (SANS). The SANS results clearly showed that there are large differences even between samples of the DT750 superalloy produced using different facilities. The modified heat treat...

In the last decade, a lot of effort has been paid to optimising the thermomechanical processing of TRIP steels that stands for transformation induced plasticity. The precise characterization of the resulting multiphase microstructure of low alloyed TRIP steels is of great importance for the interpretation and optimisation of their mechanical proper...

Commercial low-carbon steel AISI 1010 was subjected to Equal Angular Channel Pressing (ECAP) at different temperatures. The paper describes the refinement of a quiet coarse-grained ferrite microstructure to submicrocrystalline range by large plastic strain. The steel was deformed in an ECAP die with a channel angle φ = 90°, at different temperature...

Commercial purity aluminium (99.99 %) plates were processed with a severe plastic deformation technique - the Constrained Groove Pressing (CGP) at room temperature. It has been reported that using this technique, the coarse structure of pure aluminium can be refined to submicron ranges. The plates prior to CGP had a coarse-grained recrystallized st...

The precise characterization of the multiphase microstructure of low alloyed TRIP steels is of great importance for the interpretation and optimisation of their mechanical properties. In-situ neutron diffraction experiment was employed for monitoring of conditioned austenite transformation to ferrite, and also for retained austenite stability evalu...

Purpose: The aim of this study is to contribute to a better understanding of the role of the key factors governing the formation of multiphase TRIP aided steel.Design/methodology/approach: The present work reports the results of in-situ neutron diffraction experiments focused on monitoring the phase evolution in three TRIP steel samples subjected t...

By application of thermomechanical controlled rolling and accelerated cooling, the ferrite grain refinement is limited to levels of ~ 5 μm in steels. The strain assisted or strain induced transformation could be considered for the refining process. The present work, likewise, deals with grain refinement of medium carbon steel containing 0.45 wt. pc...

High strength and ductility of the TRIP steels is often attributed to the transformation induced plasticity effect resulting from the strain induced martensitic transformation of the retained austenite in the bainite microstructure. The present work reports results of in-situ neutron diffraction experiments focused on monitoring the phase evolution...

It was found that the annealed microstructure resulting from only one or two steps of hot working in NiMoCr alloy was not uniform throughout the specimens as desired. In order to obtain more uniform grain structures an additional cold working was utilized. The following annealing process was supposed to achieve uniform recrystallized grain structur...

By application of thermomechanically controlled rolling and accelerated cooling, the ferrite grain refinement is limited to levels of ∼ 5 μm in steels. The strain assisted or strain induced transformation could be considered for the refining process. The present work, likewise, deals with grain refinement of medium carbon steel containing 0.45 wt p...

The deformation behaviour of the wrought nickel base superalloy EI698 VD has been investigated in condition of low cycle fatigue. The tensile hold periods, imposing a constant stress into fatigue loading, have been introduced at the maximum stress value. The individual hold periods were in the range of 1 minute to 10 hours. The fatigue tests were o...

When exposed for long time at elevated temperatures of 430 and 650 degreesC the nickel base superalloy EI698 VD can experience a significant decrease in creep resistance. The cause of the creep degradation of nickel base superalloy is generally attributed to the microstructural instability at prolonged high temperature exposure. In this article, th...

When exposed for long time at elevated temperatures of 430 C and 650 C the nickelbase superalloy EI 698 VD can experience a significant decrease in the creep. The cause of the creep degradation of nickel base superalloy has never been unequivocally explained, but it has generally attributed to the microstructural instability at prolonged high tempe...

An excellent combination of high strength and formability can be obtained in a Si-Mn TRIP steels when processed by thermomechanical treatment consisting of high temperature deformation followed by isothermal holding in the bainite region and cooling to room temperature. Microstructure of these steels consists of ferrite, bainite and retained austen...

This paper describes the effect of different thermomechanical processing (TMP) conditions on the evolution of the recrystallized structure of NiMoCr alloy. The hot working conditions and various heat treatment parameters were employed in order to influence the recrystallization process of the alloy. The changes in microstructure resulting from test...

The SANS experiment was a crucial part of a broader investigation of the long-time structural stability of the polycrystalline Ni-base superalloy and its effect on the subsequent creep characteristics. The results of the creep tests have shown that a long isothermal exposure at temperatures of 430 C and 650 C up to 25000 h changed the deformation a...

In materials science and solid state physics progress has been made in many cases by one of the following approaches. Either by developing and applying new methods of investigation or by preparing materials with novel structures and/or properties. The process of materials properties improving or discovery of new materials represents developments re...

A brief description of an improvement of a special evaluation procedure for treatment of data from anisotropic Small-Angle Neutron Scattering (SANS) is presented. A spatial orientation distribution of particles, the improved calculation of a size distribution, the option to fit a data from a sample containing two types of particles as well as the r...

A non-destructive investigation of precipitate morphology in creep-exposed (900°C/300MPa) CMSX3 single-crystal (Cr 8.0, Co 4.0, Mo 0.5, Al 5.7, W 9.0, Ti 0.7, Ta 5.7, Ni balance; wt%) using pin-hole SANS is presented. The experiment provided information on microstructural parameters for samples of 5mm effective thickness.

High-resolution neutron diffraction technique was applied in investigations of thermal fatigue of Ni-base superalloy. Precise measurements of diffraction profiles and an analysis of their shape were used for evaluation of internal microstrains resulting from both phase specific stress due to lattice misfit of γ′/γ phases and plastic deformation aft...

The effect of different initial microstructures of single crystal nickel base superalloy, frequently used as blade material for gas turbines, defined by gamma prime morphology, has been investigated under the creep and creep-fatigue conditions at 900°C and 500 MPa. For cyclic loading the wave form of stress as a function of time was of trapezoidal...

In order to yield better mechanical properties of QStE 380 TM microalloyed steeel grade, the optimization of the rolling process in laboratory experiment and mill trials were carried out. For the purpose of optimizing the rolling process parameters, the studies involving simulation of reheating temperature, rolling process conditions in austenite r...

The mutual relationship between mechanical properties and microstructure changes in Al-A14C3 composite system is characterised by tensile test in wide range of testing temperatures. The dominant mechanism of plastic deformation at the deformation temperatures up to 300°C regardless of used strain rate was dislocation glide. In temperature region fr...

TEM images of thin foils with quasi-globular particles are examined by means of two methods of spatial statistics. The spatial arrangement of particle reference points is described by means of its shape with quadrat count statistics and by polygonal method (the analysis of the Voronoi mosaic generated by patterns of particle reference points). A go...

The influence of different heat treatments on the microstructure of ordered cuboidal γ′ precipitates in the ZS26 superalloy (wt%: Ni 64, W 11, Co 9, Al 6, Cr 5, Nb 1.5, Ti 1, Mo 1, V 1) was studied by small-angle neutron scattering. The average shape and size of the precipitates were determined by modelling the scattering curves and by fitting them...

High temperature creep, isothermal cyclic creep, and creep with additional thermal-mechanical fatigue stress component were performed on a wrought nickel base superalloy. The effect of the individual tensile hold periods as well as combined effect of hold periods and the thermo-mechanical fatigue stress effect was studies. The deformation behaviour...

The static and the cyclic creep load-controlled tests of the nickel base single-crystal superalloy, CMSX 3 have been studied. In this study, two different testing procedures of cyclic creep were carried out under specific loading schedules defined by the stress amplitude, the stress range, stress ratio, and cycling frequency. The different cycling...

In the presented work the differences in plasticity and fracture micromechanism were investigated and analyzed in the Al-Al4C3 system with 4 vol.% of Al4C3 by tensile testing at 450°C and two strain rates. At high strain rate 10-1 s-1 a superplastic-like behaviour has been observed, showing large uniform strain. The microstructure is polygonized, t...

The static and cyclic creep load controlled tests of as-cast and heat treated single crystal nickel base superalloy CMSX 3 have been studied. Two different testing procedures were adopted. One is cyclic creep test with different hold times at maximum stress amplitude, and the other cyclic creep procedure is in which the mean stress was held constan...

High temperature components assembled in aircraft turbines are subjected to complex stress, including thermal stress, stress originating from centrifugal force and high frequency vibration stress. Recently increased attention has been paid to the study of creep and fatigue interaction which appears to be an important factor in the prediction of the...

The industrially manufactured transformer steel on the Fe-3% Si basis grains its final characteristics during the secondary recrystallization process, where the expressive Goss texture {110} 〈9001〉 is formed. However, the optimal characteristics of the finished transformer strip depend on the microstructure and texture parameters of the hot rolled...

The creep and creep-fatigue tests with holding times at upper stress amplitude are carried out at temperature 900 °C on single crystal superalloy CMSX-3 with nickel base. The experimental results show that the incorporation of hold time at cyclic creep test has strong effect on fracture lifetime and strain of tested samples. The resulted strain val...

The effect of different initial microstructures defined by various precipitates γ morphology was investigated at the creep/fatigue conditions by 900 °C and 500 MPa. The waveform of stress as a function of time for cyclic loading was of trapezoidal shape with a hold time 10 seconds at the upper stress level. TEM was employed to examine the deformati...

Heat treated specimens of single crystal nickel base superalloy were submitted to tension creep at the temperature of 900°C. The deformation process was investigated at different states of creep. In the matrix hardened by bimodal precipitates the development of dislocation structure and precipitates morphology changes were studied by means of TEM o...

Microstructural heterogeneity was examined in the as-cast microstructure of directionally solidified ZS 26 nickel based superalloy. The distribution of elements in primary and secondary dendrite growth direction was determined by quantitative EDX analysis. Measurements of elemental partitioning show an appaerent segregation behaviour of Al, Ti, W,...

The effect of structure modification on creep characteristics of nickel based superalloy EI 698 VD has been studied. The substructure changes were caused by variation of the temperature and time parameters in solution treatments and in precipitation annealing process of the alloy. Through the change of gamma prime morphology and extent of M(23)C(6)...

The paper reports very briefly the major trends and developments in high performance materials, including not only metallic alloys but also engineering plastics and ceramics. The widely organized research and development not only seeks to find out new materials but also actively promotes their use in applications involving the substitution of tradi...

The lamellar precipitation, morphology and crystallography relationship in HK 40 alloy with a high content of nitrogen 0.065-0.155 wt.% were studied. According to the results, the precipitates are M 23C 6 and they have the following orientation relationship with the matrix {001} M(23)C(6)∥{001} γ, 〈001〉 M(23)C(6)∥〈001〉 γ. The lower nitrogen limit a...

The aim of this work is to evaluate, on the basis of comparing the results obtained for specimens subjected to the same treatment, the deformation process and changes in the substructure of specimens which satisfy the prescribed creep test conditions, and specimens which failed prematurely prior to reaching the given time limit. Experimental result...

The preparation of crystalline tapes from polycomponent materials can be realised by rapid cooling from the melt. The initial microstructures of the nickel superalloy were similar for all disc speeds. The results make it possible to evaluate the relationships of solidification at high cooling rates which can be related to the solidification process...

The effect of reaustenitization of tempered martensite on the elimination of embrittlement in the martensite of an Fe-Ni-C model alloy was investigated. The results suggest that intercrystalline embrittlement caused by the presence of particles of complex intermetallic phases of Fe with Mn, Ni, and Si over the grain boundaries of the initial austen...

It has been founc that martensite embrittlement of a model Fe-Ni-C alloy after annealing of austenite at 600 degree C for 1 hour is caused by segregation and precipitation processes which take place during heat treatment of the alloy. The presence of complex Fe-based intermetallic phases with Ni, Si, and Mn has been demonstrated. The precipitation...

It has been found experimentally, using a model Fe-Ni-C alloy, that reaustenitizing heating after tempering of martensite causes positive changes in its mechanical and plastic properties. The principal cause for these improvements was found to be the presence of disperse cementite particles and increased intensity of dislocations. Martensite formed...

The deformation behaviour and damage mechanisms of the wrought nickel based superalloy EI 698 VD has been investigated under creep/fatigue loading conditions. The alloy was subjected to a load controlled isothermal low cycle fatigue at 650 o C with superimposed hold periods of constant tensile load simulating creep stress components. The introduced...