Abstract Sintering of Cr-prealloyed PM steels requires atmospheres with good quality – low oxygen potential – to achieve satisfactory sintering results. But during heating even the best atmospheres may be oxidizing, the system turns to reducing conditions only at high temperatures, which can be monitored by thermal analysis. During the dewaxing process, oxidizing conditions are favourable for effective dewaxing without sooting and blistering. However, this may result in some oxygen pickup during heating, and then the final properties of the produced parts may be strongly influenced by this intermediate oxidation. This study demonstrates the behaviour of artificially oxidized steels (Fe-C and Fe3Cr-0.5Mo-C) during the sintering process by stepwise sintering. Iron and steel powder were slightly oxidized and then pressed and sintered at different temperatures. In parallel, as a second approach, pressed samples were oxidized and then sintered. Density, hardness and impact energy were measured and dilatometry/MS was used for online monitoring of the sintering process. The starting oxygen content of 0.20 to 0.30 wt% is high enough to change the sintering behaviour of the materials, but still leads to rather good properties. Thermal analysis showed that most of the oxygen picked up was present as iron oxides on the surface which were reduced by hydrogen at rather low temperatures, confirming that these were iron oxides, which also holds for the Cr-prealloyed variant. The biggest influence on the final performance was exerted by the final carbon content and the microstructural development of the material.
{"title":"Study on Sintering of Artificially Oxidized Steel Compacts","authors":"C. Gierl-Mayer, T. Stepan, J. Sun, H. Danninger","doi":"10.1515/pmp-2019-0002","DOIUrl":"https://doi.org/10.1515/pmp-2019-0002","url":null,"abstract":"Abstract Sintering of Cr-prealloyed PM steels requires atmospheres with good quality – low oxygen potential – to achieve satisfactory sintering results. But during heating even the best atmospheres may be oxidizing, the system turns to reducing conditions only at high temperatures, which can be monitored by thermal analysis. During the dewaxing process, oxidizing conditions are favourable for effective dewaxing without sooting and blistering. However, this may result in some oxygen pickup during heating, and then the final properties of the produced parts may be strongly influenced by this intermediate oxidation. This study demonstrates the behaviour of artificially oxidized steels (Fe-C and Fe3Cr-0.5Mo-C) during the sintering process by stepwise sintering. Iron and steel powder were slightly oxidized and then pressed and sintered at different temperatures. In parallel, as a second approach, pressed samples were oxidized and then sintered. Density, hardness and impact energy were measured and dilatometry/MS was used for online monitoring of the sintering process. The starting oxygen content of 0.20 to 0.30 wt% is high enough to change the sintering behaviour of the materials, but still leads to rather good properties. Thermal analysis showed that most of the oxygen picked up was present as iron oxides on the surface which were reduced by hydrogen at rather low temperatures, confirming that these were iron oxides, which also holds for the Cr-prealloyed variant. The biggest influence on the final performance was exerted by the final carbon content and the microstructural development of the material.","PeriodicalId":52175,"journal":{"name":"Powder Metallurgy Progress","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67337521","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Traditionally, powder metallurgy has been based on two major industrial sectors – ferrous precision parts and hardmetals. Both of them relied heavily on the automotive industry, with focus on internal combustion engines. Today, there is an increasing trend towards alternative drivetrain systems, and powder metallurgy faces the challenge to find new applications to replace those lost with the decrease of classical internal combustion drives. In this presentation it is shown that the main strength of powder metallurgy lies in its enormous flexibility regarding materials, geometries, processing and properties. This enables PM to adapt itself to changing requirements in a changing industrial environment. Examples given are PM parts in alternative drivetrain systems, new alloying concepts and processing routes offering distinct advantages. With hardmetals, innovative microstructures as well as sophisticated coatings offer increased lifetime, applications ranging from metalworking to rockdrilling and concrete cutting. A particularly wide area is found in functional materials which range from components for high power switches to such for fuel cells. Soft and hard magnets are accessible by PM with particularly good properties, PM having in part exclusivity in that respect, such as for NdFeB superhard magnets as well as soft magnetic composites (SMCs). Metal injection moulding (MIM) is gaining further ground, e.g. in the medical area which is a fast-growing field, due to demographic effects. Finally, most additive manufacturing techniques are powder based, and here, the knowledge in powder handling and processing available in the PM community is essential for obtaining stable processes and reliable products. Conclusively it can be stated that PM is on the way to fully exploit its potential far beyond its traditional areas of applications.
{"title":"What Will Be the Future of Powder Metallurgy?","authors":"H. Danninger","doi":"10.1515/pmp-2018-0008","DOIUrl":"https://doi.org/10.1515/pmp-2018-0008","url":null,"abstract":"Abstract Traditionally, powder metallurgy has been based on two major industrial sectors – ferrous precision parts and hardmetals. Both of them relied heavily on the automotive industry, with focus on internal combustion engines. Today, there is an increasing trend towards alternative drivetrain systems, and powder metallurgy faces the challenge to find new applications to replace those lost with the decrease of classical internal combustion drives. In this presentation it is shown that the main strength of powder metallurgy lies in its enormous flexibility regarding materials, geometries, processing and properties. This enables PM to adapt itself to changing requirements in a changing industrial environment. Examples given are PM parts in alternative drivetrain systems, new alloying concepts and processing routes offering distinct advantages. With hardmetals, innovative microstructures as well as sophisticated coatings offer increased lifetime, applications ranging from metalworking to rockdrilling and concrete cutting. A particularly wide area is found in functional materials which range from components for high power switches to such for fuel cells. Soft and hard magnets are accessible by PM with particularly good properties, PM having in part exclusivity in that respect, such as for NdFeB superhard magnets as well as soft magnetic composites (SMCs). Metal injection moulding (MIM) is gaining further ground, e.g. in the medical area which is a fast-growing field, due to demographic effects. Finally, most additive manufacturing techniques are powder based, and here, the knowledge in powder handling and processing available in the PM community is essential for obtaining stable processes and reliable products. Conclusively it can be stated that PM is on the way to fully exploit its potential far beyond its traditional areas of applications.","PeriodicalId":52175,"journal":{"name":"Powder Metallurgy Progress","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48452207","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Due to the increasing usage of powder metallurgy (PM), there is a demand to evaluate and improve the mechanical properties of PM parts. One of the most important mechanical properties is wear behavior, especially in parts that are in contact with each other. Therefore, the choice of materials and select manufacturing parameters are very important to achieve proper wear behavior. So, prediction of wear resistance is important in PM parts. In this paper, we try to investigate and predict the wear resistance (volume loss) of PM porous steels according to the affecting factors such as: density, force and sliding distance by artificial neural network (ANN). ANN training was done by a multilayer perceptron procedure. The comparison of the results estimated by the ANN with the experimental data shows their proper matching. This issue confirms the efficiency of using method for prediction of wear resistance in PM steel parts.
{"title":"Prediction of Wear Behavior in Porous Sintered Steels: Artificial Neural Network Approach","authors":"H. Abdoos, A. Tayebi, M. Bayat","doi":"10.1515/pmp-2018-0012","DOIUrl":"https://doi.org/10.1515/pmp-2018-0012","url":null,"abstract":"Abstract Due to the increasing usage of powder metallurgy (PM), there is a demand to evaluate and improve the mechanical properties of PM parts. One of the most important mechanical properties is wear behavior, especially in parts that are in contact with each other. Therefore, the choice of materials and select manufacturing parameters are very important to achieve proper wear behavior. So, prediction of wear resistance is important in PM parts. In this paper, we try to investigate and predict the wear resistance (volume loss) of PM porous steels according to the affecting factors such as: density, force and sliding distance by artificial neural network (ANN). ANN training was done by a multilayer perceptron procedure. The comparison of the results estimated by the ANN with the experimental data shows their proper matching. This issue confirms the efficiency of using method for prediction of wear resistance in PM steel parts.","PeriodicalId":52175,"journal":{"name":"Powder Metallurgy Progress","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46172059","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. de Oro Calderon, M. Jaliliziyaeian, J. Dunkley, C. Gierl-Mayer, H. Danninger
Abstract The Masteralloy (MA) alloying route has a great potential for reducing the alloying costs in sintered steels, while allowing the introduction of innovative alloying systems. However, in order to achieve an efficient use of the alloying elements, the particle sizes needed are often below 25 µm, which means that for standard gas atomization a significant fraction of the batch has to be discarded or at least recycled. This work evaluates the performance of steels containing MA powders obtained with a novel atomization technique (Ultra-High-Pressure Water atomization) that allows the production of low-cost powders with low oxygen contents, rounded morphologies and mean particle sizes as low as 6 microns. Mechanical properties, dimensional variations and interstitial contents were measured in steels containing different MA compositions sintered at either 1120 °C or1250 ºC in N2-5H2 atmospheres. Already with less than 3 wt.% of alloying elements these steels present excellent combinations of properties, reaching strength levels of 560-915 MPa and hardness 220-260 HV10, combined with elongations of 1.3-3.2% and impact energies around 20-30 J/cm2.
{"title":"New Chances for the Masteralloy Approach","authors":"R. de Oro Calderon, M. Jaliliziyaeian, J. Dunkley, C. Gierl-Mayer, H. Danninger","doi":"10.1515/pmp-2018-0014","DOIUrl":"https://doi.org/10.1515/pmp-2018-0014","url":null,"abstract":"Abstract The Masteralloy (MA) alloying route has a great potential for reducing the alloying costs in sintered steels, while allowing the introduction of innovative alloying systems. However, in order to achieve an efficient use of the alloying elements, the particle sizes needed are often below 25 µm, which means that for standard gas atomization a significant fraction of the batch has to be discarded or at least recycled. This work evaluates the performance of steels containing MA powders obtained with a novel atomization technique (Ultra-High-Pressure Water atomization) that allows the production of low-cost powders with low oxygen contents, rounded morphologies and mean particle sizes as low as 6 microns. Mechanical properties, dimensional variations and interstitial contents were measured in steels containing different MA compositions sintered at either 1120 °C or1250 ºC in N2-5H2 atmospheres. Already with less than 3 wt.% of alloying elements these steels present excellent combinations of properties, reaching strength levels of 560-915 MPa and hardness 220-260 HV10, combined with elongations of 1.3-3.2% and impact energies around 20-30 J/cm2.","PeriodicalId":52175,"journal":{"name":"Powder Metallurgy Progress","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43193688","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Ebrahimnia, Hamzeh Baghjari, M. Ajdari, Alireza Hajesmaeli, M. Hojati
Abstract Refurbishment of worn Dies is an interesting research area which also has high economic benefit. Material which is used in PM dies for compacting powders are high carbon steel which have very low weldabilitis. Due to the high hardness, high carbon content and martensitic microstructure, these Dies are very sensitive to the thermal shock produced from fusion welding. For successfully refurbishing the worn Dies, Fine spark deposition was used for deposition of a new layer on the cold work 1.2436 steel. Different heat inputs were used for deposition of nickel based material and finally microstructure and HAZ were studied. Results show the HAZ area is very narrow, free from cracks and HAZ microstructure is similar to the base metal. GTAW welding using same filler metal induced many cracks in HAZ of weld which is detrimental to the refurbished Die performance. Results show increasing heat input in Fine spark deposition can results in crack formation in HAZ even if the weld pool does not occurred in base metal. However these cracks are much smaller than those occurred in GTAW.
{"title":"Application of a Low Heat Input Deposition Process for Refurbishment of Worn PM Forming Dies Using Fe-Ni Based Filler Metal","authors":"M. Ebrahimnia, Hamzeh Baghjari, M. Ajdari, Alireza Hajesmaeli, M. Hojati","doi":"10.1515/pmp-2018-0013","DOIUrl":"https://doi.org/10.1515/pmp-2018-0013","url":null,"abstract":"Abstract Refurbishment of worn Dies is an interesting research area which also has high economic benefit. Material which is used in PM dies for compacting powders are high carbon steel which have very low weldabilitis. Due to the high hardness, high carbon content and martensitic microstructure, these Dies are very sensitive to the thermal shock produced from fusion welding. For successfully refurbishing the worn Dies, Fine spark deposition was used for deposition of a new layer on the cold work 1.2436 steel. Different heat inputs were used for deposition of nickel based material and finally microstructure and HAZ were studied. Results show the HAZ area is very narrow, free from cracks and HAZ microstructure is similar to the base metal. GTAW welding using same filler metal induced many cracks in HAZ of weld which is detrimental to the refurbished Die performance. Results show increasing heat input in Fine spark deposition can results in crack formation in HAZ even if the weld pool does not occurred in base metal. However these cracks are much smaller than those occurred in GTAW.","PeriodicalId":52175,"journal":{"name":"Powder Metallurgy Progress","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46274312","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. Haubner, E. Rauchenwald, M. Lessiak, R. Pitonak, R. Weissenbacher
Abstract Investigations of hard and wear resistant materials have a long tradition to increase the performance and profitability of machining applications. The evolution started with WC-Co hardmetal alloys, which were produced by PM technology, followed by CVD coatings on hardmetal tools. The first CVD coatings applied were TiC, TiN and Al2O3. The properties of these coatings could be optimized by varying the crystal size, crystal orientation but also combination of the materials in multilayer systems. Nowadays, about 85% of all hardmetal tools are coated.During the last years, driven by PVD coatings showing good performance (e.g. TiAlN), the search for new CVD coatings was intensified. Medium temperature (MT) CVD processes for TiCN allowed the deposition of TiCN crystals with different composition side by side. Due to this microstructure the adhesion between single layers in new multilayer coatings like TiN/MT-TiCN/Al2O3/TiN could be increased. Novel (Ti,Al)N coatings were developed, showing a nanolamellae microstructure consisting of self-assembled (Ti,Al)N with different composition. For the future there is still plenty to investigate. The already existing coatings and coating systems have to be optimized for the various machining applications. To find new types of CVD coatings, we look for chemical reactions practicable for its use in CVD equipment.
{"title":"Novel High-Performance CVD Coatings for Machining Applications","authors":"R. Haubner, E. Rauchenwald, M. Lessiak, R. Pitonak, R. Weissenbacher","doi":"10.1515/pmp-2018-0015","DOIUrl":"https://doi.org/10.1515/pmp-2018-0015","url":null,"abstract":"Abstract Investigations of hard and wear resistant materials have a long tradition to increase the performance and profitability of machining applications. The evolution started with WC-Co hardmetal alloys, which were produced by PM technology, followed by CVD coatings on hardmetal tools. The first CVD coatings applied were TiC, TiN and Al2O3. The properties of these coatings could be optimized by varying the crystal size, crystal orientation but also combination of the materials in multilayer systems. Nowadays, about 85% of all hardmetal tools are coated.During the last years, driven by PVD coatings showing good performance (e.g. TiAlN), the search for new CVD coatings was intensified. Medium temperature (MT) CVD processes for TiCN allowed the deposition of TiCN crystals with different composition side by side. Due to this microstructure the adhesion between single layers in new multilayer coatings like TiN/MT-TiCN/Al2O3/TiN could be increased. Novel (Ti,Al)N coatings were developed, showing a nanolamellae microstructure consisting of self-assembled (Ti,Al)N with different composition. For the future there is still plenty to investigate. The already existing coatings and coating systems have to be optimized for the various machining applications. To find new types of CVD coatings, we look for chemical reactions practicable for its use in CVD equipment.","PeriodicalId":52175,"journal":{"name":"Powder Metallurgy Progress","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1515/pmp-2018-0015","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46938603","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The composite based on the microns iron size powder and MgO nanopowder was prepared using pressing followed by conventional and microwave sintering. Microstructure of the composite was investigated to evaluate the changes induced by different sintering technology. Young’s modulus, flexural strength and hardness of composites were analyzed to investigate the mechanical properties in dependence on MgO content, as well as in dependence on the sintering method. Microstructure and mechanical properties as well as functional magnetic properties of prepared composites are discussed in the paper. The main benefit of microwave heating found within process time shortening was confirmed in the case of the microwave sintered Fe/MgO composite.
{"title":"Microstructure and Mechanical Properties of Fe/MgO Micro-Nano Composite for Electrotechnical Applications","authors":"Radovan Bureš, M. Fáberová, P. Kurek","doi":"10.1515/pmp-2018-0011","DOIUrl":"https://doi.org/10.1515/pmp-2018-0011","url":null,"abstract":"Abstract The composite based on the microns iron size powder and MgO nanopowder was prepared using pressing followed by conventional and microwave sintering. Microstructure of the composite was investigated to evaluate the changes induced by different sintering technology. Young’s modulus, flexural strength and hardness of composites were analyzed to investigate the mechanical properties in dependence on MgO content, as well as in dependence on the sintering method. Microstructure and mechanical properties as well as functional magnetic properties of prepared composites are discussed in the paper. The main benefit of microwave heating found within process time shortening was confirmed in the case of the microwave sintered Fe/MgO composite.","PeriodicalId":52175,"journal":{"name":"Powder Metallurgy Progress","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47779102","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract This research was focused on mixing of submicron cemented carbide (WC-Co-VC) powder and binder. WC-Co-VC powder particle size and morphology were analyzed by laser diffraction and field emission scanning electron microscopy. The WC-Co-VC powder was kneaded with a paraffin wax based binder system. Based on critical solid loading, the feedstock with different solid loadings between 49 to 51 vol.% was prepared. Finally, the flow behavior of different feedstocks was investigated. Morphology of powder revealed that the particles of powder are slightly agglomerated and irregular in shape. The result of mixing indicted that the torque value increases as the solid loading increase from 49 vol.% to 51 vol.%. The feedstock exhibited homogeneity and the powder particles are homogenously coated with binder. The feedstock with solid loading of 51 vol.% is sensitive to temperature and showed high viscosity values. The feedstock with solid loadings of 49 and 50 vol.% had good compatibility and flow characteristics.
{"title":"Investigation on Feedstock Preparation for Micro-Cemented Carbide Injection Molding","authors":"A. Fayyaz, N. Muhamad, A. Sulong","doi":"10.1515/pmp-2018-0010","DOIUrl":"https://doi.org/10.1515/pmp-2018-0010","url":null,"abstract":"Abstract This research was focused on mixing of submicron cemented carbide (WC-Co-VC) powder and binder. WC-Co-VC powder particle size and morphology were analyzed by laser diffraction and field emission scanning electron microscopy. The WC-Co-VC powder was kneaded with a paraffin wax based binder system. Based on critical solid loading, the feedstock with different solid loadings between 49 to 51 vol.% was prepared. Finally, the flow behavior of different feedstocks was investigated. Morphology of powder revealed that the particles of powder are slightly agglomerated and irregular in shape. The result of mixing indicted that the torque value increases as the solid loading increase from 49 vol.% to 51 vol.%. The feedstock exhibited homogeneity and the powder particles are homogenously coated with binder. The feedstock with solid loading of 51 vol.% is sensitive to temperature and showed high viscosity values. The feedstock with solid loadings of 49 and 50 vol.% had good compatibility and flow characteristics.","PeriodicalId":52175,"journal":{"name":"Powder Metallurgy Progress","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48083687","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract In situ characterization of the sintering process is a difficult task, in particular for systems without pronounced dimensional changes. Dilatometry is not too helpful in those cases, and therefore other properties have to be recorded. In the present study, sintering of ferrous powder compacts was studied in situ by measuring the thermal diffusivity a using a laser flash apparatus. This property is a measure to characterise the heat flow through a material; it depends on the contact area between the particles and thus reveals their change during sintering. It is shown that the change of a during sintering of ferrous compacts is much less pronounced than in the case of cemented carbides which is not surprising when regarding the widely differing porosity changes. The results are however in good agreement with expectations when considering some experimental limitations. The trend for the thermal conductivity λ. which can be calculated from a, the specific heat and the density, is in good agreement with that found for the electrical conductivity, both properties being linked through Wiedemann-Franz’ law.
{"title":"Studying the Progress of Sintering in Ferrous Powder Compacts by In-Situ Measuring the Thermal Conductivity","authors":"H. Danninger, G. Leitner, C. Gierl-Mayer","doi":"10.1515/pmp-2018-0009","DOIUrl":"https://doi.org/10.1515/pmp-2018-0009","url":null,"abstract":"Abstract In situ characterization of the sintering process is a difficult task, in particular for systems without pronounced dimensional changes. Dilatometry is not too helpful in those cases, and therefore other properties have to be recorded. In the present study, sintering of ferrous powder compacts was studied in situ by measuring the thermal diffusivity a using a laser flash apparatus. This property is a measure to characterise the heat flow through a material; it depends on the contact area between the particles and thus reveals their change during sintering. It is shown that the change of a during sintering of ferrous compacts is much less pronounced than in the case of cemented carbides which is not surprising when regarding the widely differing porosity changes. The results are however in good agreement with expectations when considering some experimental limitations. The trend for the thermal conductivity λ. which can be calculated from a, the specific heat and the density, is in good agreement with that found for the electrical conductivity, both properties being linked through Wiedemann-Franz’ law.","PeriodicalId":52175,"journal":{"name":"Powder Metallurgy Progress","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47701076","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. T. Mekonone, I. Cristofolini, W. Pahl, A. Molinari
Abstract Carburizing increases the contact fatigue resistance of sintered steels, but the surface hardening may result the formation of surface brittle cracks due to the combined effect of high hardness and porosity. The effect of carburizing on the embrittlement of the case of a 7.3 g/cm3 1.5%Mo - 0.25%C sintered steel was studied. The phenomenon was analyzed theoretically and verified by experiments. The resistance of the carburized steel to surface brittle cracking increases with the load bearing surface and the decrease of the maximum pore size, of the surface microhardness and the friction coefficient. The theoretical analysis was implemented in a design procedure for parts subject to contact stresses.
{"title":"Surface Hardening Vs. Surface Embrittlement in Carburizing of Porous Steels","authors":"S. T. Mekonone, I. Cristofolini, W. Pahl, A. Molinari","doi":"10.1515/pmp-2018-0003","DOIUrl":"https://doi.org/10.1515/pmp-2018-0003","url":null,"abstract":"Abstract Carburizing increases the contact fatigue resistance of sintered steels, but the surface hardening may result the formation of surface brittle cracks due to the combined effect of high hardness and porosity. The effect of carburizing on the embrittlement of the case of a 7.3 g/cm3 1.5%Mo - 0.25%C sintered steel was studied. The phenomenon was analyzed theoretically and verified by experiments. The resistance of the carburized steel to surface brittle cracking increases with the load bearing surface and the decrease of the maximum pore size, of the surface microhardness and the friction coefficient. The theoretical analysis was implemented in a design procedure for parts subject to contact stresses.","PeriodicalId":52175,"journal":{"name":"Powder Metallurgy Progress","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49535497","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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