Papers by Bojan Podgornik
Wear, May 1, 2001
In the present study, samples made of AISI 4140 steel pre-treated with plasma nitriding and coate... more In the present study, samples made of AISI 4140 steel pre-treated with plasma nitriding and coated with different PVD coatings (TiN, TiAlN and ta-C) were investigated in terms of their microhardness, surface roughness, scratch adhesion and dry sliding wear resistance. Wear tests, in which duplex-treated pins were mated to hardened ball bearing steel discs, were performed with a pin-on-disc machine. To examine the influence of the nitrided zone on the performance of the coating-substrate composite, coatings were deposited on hardened as well as on plasma nitrided samples, prepared under different nitriding conditions.
Applied Surface Science, 2016
Wear, Feb 1, 2009
The aim of the present research was to investigate influence of surface preparation on roughness ... more The aim of the present research was to investigate influence of surface preparation on roughness parameters and correlation between roughness parameters and friction and wear. First the correlation between different surface preparation techniques and roughness parameters was investigated. For this purpose 100Cr6 steel plate samples were prepared in terms of different average surface roughness, using different grades of grinding, polishing, turning and milling. Different surface preparation techniques resulted in different R a values from 0.02 to 7 m. After this, correlation between surface roughness parameters and friction and wear was investigated. For this reason dry and lubricated pin-on-disc tests, using different contact conditions, were carried out, where Al 2 O 3 ball was used as counter-body. It was observed that parameters R ku , R sk , R pk and R vk tend to have influence on coefficient of friction.
Surf Interface Anal, 2008
In the past, adequate functionality of high-performance components would have been impossible wit... more In the past, adequate functionality of high-performance components would have been impossible without advanced lubricant additive chemistry and proper lubricant formulation. Especially anti-wear (AW) and extreme-pressure (EP) additives are crucial in minimising friction and wear and protecting contact surfaces under severe contact conditions. Introduction of diamond-like carbon (DLC) coatings, on the other hand, opens further possibilities in improving performance of highly loaded components, which can no longer be achieved only by lubricant design.
Wear, 2003
ABSTRACT The aim of this work was to investigate the potential of using hard physical vapour depo... more ABSTRACT The aim of this work was to investigate the potential of using hard physical vapour deposition (PVD) coatings on forming tools, as well as to determine the influence of plasma nitriding on the load-carrying capacity and wear resistance of coated tool surfaces. A load-scanning test rig was used for evaluation, where duplex treated cold work tool steel samples were loaded against soft austenitic stainless steel and hardened ball bearing steel, respectively. Four different coatings (TiN, TiB2, TaC and DLC) and two substrate treatments (hardening and plasma nitriding in two different gas mixtures) were included.Plasma nitriding alone significantly improved the friction, wear, and anti-sticking properties of the tool steel. PVD coating, and especially PVD coating of nitrided tool steel further improved the performance. Therefore, from the point of view of tool life as well as work peace surface quality, the DLC coating with its excellent anti-sticking properties and sufficiently good wear resistance represent the best solution for forming tool applications of austenitic stainless steel.
Surface Coatings Technology, 2007
By providing excellent frictional properties and greatly improving wear resistance of sliding con... more By providing excellent frictional properties and greatly improving wear resistance of sliding contact surfaces, diamond-like carbon coatings (DLC) offer a great opportunity for improving performance and durability, and reducing frictional losses in many mechanical systems. However, for the successful application of coated machine components, coatings have to perform reliably under dry and oil-lubricated conditions, with the majority of machine components still being oil-lubricated and operating under diverse contact conditions.
Materiali in tehnologije, 2016
Hard coatings are becoming increasingly important in the field of machine components. Because the... more Hard coatings are becoming increasingly important in the field of machine components. Because they are able to improve the wear resistance and provide excellent frictional properties, diamond-like, hard carbon (DLC) coatings provide a great opportunity for improving the durability and reducing the frictional losses of machine components. However, the majority of machine components operate under lubricated conditions, where interactions between the surface and the lubricant play a significant role. Especially under boundary lubrication conditions, these interactions will determine the tribological behaviour of the contact. One of the main factors that limits the use of hard coatings in machine-component applications is the lack of knowledge relating to how these inert coatings perform under lubricated conditions with today's oils, which were originally designed for steel/steel contact situations. The aim of this study was to investigate the influence of conventional extreme-pressure (EP) and anti-wear (AW) additives for gearbox oils on the tribological performance of DLC-coated steel surfaces in the boundary lubrication regime. The results of our investigation show that the introduction of DLC coatings can also significantly improve the tribological performance of a contact under boundary lubrication conditions. Trde prevleke se poleg odrezovalnih orodij vse bolj uveljavljajo tudi na podro~ju strojnih elementov. Predvsem prevleke na osnovi trdega ogljika, ki imajo zelo dobro obrabno odpornost in nizek koeficient trenja proti razli~nim materialom, dajejo izjemne monosti za izbolj{anje obstojnosti ter zmanj{anje tornih izgub mehanskih sistemov. Po drugi strani pa ve~ina mehanskih sistemov deluje v razmerah mazanega kontakta, kjer so interakcije med kontaktno povr{ino in mazivom izredno pomembne. (e posebej v primeru mejnega mazanja je tribolo{ko vedenje kontaktnih povr{in v najve~ji meri odvisno od medsebojnega delovanja med mazivom in povr{ino ter sposobnostjo tvorjenja mejnih mazalnih plasti. Prav pomanjkanje znanja o tribolo{kem vedenju inertnih trdih prevlek v kombinaciji z razpololjivimi mazivi pa je ena od glavnih ovir za uspe{no uporabo trdih prevlek v strojni{tvu. Cilj predstavljene raziskave je bil raziskati vpliv konvencionalnih protiobrabnih aditivov (AW) in aditivov proti visokim tlakom (EP) za reduktorska olja na tribolo{ko vedenje prevlek na osnovi trdega ogljika. Rezultati kaejo, da tudi v primeru mejnega mazanja nanos prevleke na osnovi trdega ogljika mo~no izbolj{a tribolo{ke lastnosti kontaktnih povr{in. Klju~ne besede: mejno mazanje, aditivi, DLC-prevleke, trenje
Thin Solid Films, Dec 1, 2000
ABSTRACT In this study samples of AISI 4140 steel were surface treated by plasma nitriding and co... more ABSTRACT In this study samples of AISI 4140 steel were surface treated by plasma nitriding and coated with a hydrogen-free hard carbon coating, also known as tetrahedral amorphous carbon coating (ta-C). The specimens were investigated with respect to their microhardness, residual stress, coating adhesion and dry sliding wear resistance. Wear tests in which duplex-treated specimens were mated to hardened ball bearing steel were performed under unidirectional and reciprocating sliding. To examine the influence of the nitriding conditions on the performance of duplex-treated steel, the coating was deposited on hardened as well as on plasma nitrided samples, nitrided under two different nitriding conditions. The results show greatly improved sliding wear resistance of plasma-nitrided hard-coated specimens compared with un-coated and pre-hardened ones, observed for both unidirectional and reciprocating sliding. Furthermore, the hydrogen-free hard carbon coating produced a reduction in the coefficient of friction of approximately one order of magnitude. Although previous investigations showed the negative effect of a compound layer, it was found that the compound layer may act as an intermediate hard layer, leading to superior tribological properties of the composite.
Advanced Engineering Materials, 2000
Journal of Materials Processing Technology, Jun 1, 2010
The aim of this investigation was to determine the effect of different production operations and ... more The aim of this investigation was to determine the effect of different production operations and parameters on residual stress level in double-layer cast rolls. Using a hole-drilling method, residual stress depth distribution in surface layer was measured around and along the body of the double-layer cast roll after casting, heat treatment, turning and grinding. Furthermore, using different turning and grinding parameters (speed, feed), and heat treatment parameters (temperature, time), influence of these parameters on residual stress level and distribution was determined.
Tribotest, 2000
ABSTRACT In this investigation, the microstructural, mechanical and tribological properties of pl... more ABSTRACT In this investigation, the microstructural, mechanical and tribological properties of plasma and pulse plasma nitrided AISI 4140 steel have been investigated in comparison to hardened steel. The influence of nitriding case depth, as well as the presence of a compound layer, have been tribologically examined for both dry and lubricated sliding. Testing was carried out on a pin-on-disc machine in which surface-treated pins were mated to hardened ball bearing steel discs. The surface treated samples were characterised using metallographic, SEM, microhardness and profilometric techniques, before and after wear testing. The resulting wear loss and coefficient of friction were monitored as a function of load and of test time. The results showed improved tribological properties of the AISI 4140 steel after plasma and pulse plasma nitriding as compared to the hardened steel, in both dry and lubricated sliding. However, the compound layer should be removed from the surface, either by mechanical means or by decreasing the amount of nitrogen in the nitriding atmosphere, in order to avoid impairment of the tribological properties by fracture of the hard and brittle compound layer, followed by formation of hard abrasive particles.
Diamond and Related Materials, 2001
ABSTRACT Due to the very thin nature of DLC coatings, the substrate must carry the main part of t... more ABSTRACT Due to the very thin nature of DLC coatings, the substrate must carry the main part of the applied load. If the substrate has insufficient strength to carry the contact load and thus support the coating, plastic deformation will occur, leading to premature failure of the coating. The challenge to improve the properties of hard DLC coatings by thermo-chemical pre-treatment of the substrate has gained much attention in recent years, leading to a new method called duplex treatment. In the present study, a hydrogen-free hard carbon coating deposited on plasma nitrided AISI 4140 steel was investigated with respect to microhardness, residual stress, scratch adhesion and dry sliding wear resistance. The pin-on-disc results showed that nitriding of the substrate improves the wear resistance of the hydrogen-free hard carbon coating as compared to the hardened substrate. The improvement can be related to the increased load carrying capacity of the steel substrate and to improved coating to substrate adhesion.
Volume 3: Design; Tribology; Education, 2008
ABSTRACT The aim of our work was to investigate the influence of deep-cryogenic treatment paramet... more ABSTRACT The aim of our work was to investigate the influence of deep-cryogenic treatment parameters (treatment time and temperature) and austenizing temperature on the tribological performance of powder-metallurgy (P/M) high-speed steel. Special emphasis was put on abrasive wear resistance and resistance to galling under dry sliding conditions. Abrasive wear resistance was tested under reciprocating sliding conditions using alumina ball, while galling resistance against austenitic stainless steel was determined in a load-scanning test rig. Tribological test were evaluated in terms of high-speed steel wear volume, coefficient of friction under reciprocating sliding, friction variation with load, and critical load for galling initiation and stainless steel transfer layer formation.
Strojarstvo Casopis Za Teoriju I Praksu U Strojarstvu, Feb 28, 2011
Surface Engineering, 2001
ABSTRACT In the present paper, the wear resistance of dc plasma and pulse plasma nitrided AISI 41... more ABSTRACT In the present paper, the wear resistance of dc plasma and pulse plasma nitrided AISI 4140 steel has been evaluated under lubricated sliding and pitting wear conditions. Quench hardened specimens were used as a reference. The nitrided specimens were characterised using metallographic, microhardness, residual stress, and surface examination techniques. After surface treatment, lubricated sliding wear tests were performed on a pin on disc machine in which surface treated pins were loaded against hardened ball bearing steel discs. Pitting wear tests were performed on a standard FZG machine. Experimental results indicate that the wear resistance of AISI 4140 steel, especially pitting wear resistance, can be greatly improved by means of plasma and pulse plasma nitriding. However, plasma and pulse plasma nitrided AISI 4140 steel showed very similar sliding and pitting wear resistance.
Surface and Coatings Technology, Jun 1, 2004
The aim of the present work is to elucidate the influence of surface roughness on the galling pro... more The aim of the present work is to elucidate the influence of surface roughness on the galling properties of coated forming tool steel. The tribological evaluation included TiN, TiB , TaC and WCyC coatings deposited on cold work tool steel. Representing a 2 material difficult to form, austenitic stainless steel was used as a counter-material. A special test configuration made it possible to gradually increase the normal load during forward sliding strokes, and to correspondingly decrease the load during reversed ones. In this investigation, the load was varied between 100 and 1300 N, corresponding to a contact pressure between 2 and 5 GPa. The main observation is that the galling and anti-sticking properties of the tool surface dramatically improve by reducing the surface topography. Consequently, reduced substrate roughness or polishing of the contact surface after coating is highly recommended. However, selection of a carbon-based low-friction coating leads to reduced probability of worked material adhesion even at high surface roughness values and under starved lubrication. ᮊ
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Papers by Bojan Podgornik