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1

High density sintered stainless steels with improved properties

100%

Rosso M. , Actis Grande M.

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tom Vol. 21, nr 2

97-102

EN

Purpose: of this paper is the study of the properties of sintered ALSI 316L (1.4404 according to EN 10088. Sintered stainless steels occupy a prominent position in the high alloyed steels, however their properties are limited by the presence of porosity. The improvement of quality and performances of products coupled with a reduction of manufacturing costs calls for high compacting pressures, as well as high sintering temperatures. However, the possibility to fill the open porosity of sintered parts by infiltration process with a metal alloy or by the use of reactive sintering techniques can favour the production of stainless steel parts with enhanced mechanical properties and good corrosion resistance). Design/methodology/approach: Sintered AISI 316L (1.4404 according to EN 10088) stainless steel samples have been manufactured using different combinations of compacting pressure and sintering parameters (time, temperature, atmosphere), or a modified composition able to allow reactive sintering process, as well as the contact infiltration with bronze. Findings: the studies have been forwarded towards the statistical and dynamic mechanical properties, as well as the corrosion behavior. Lowering the porosity level and increasing the sintering degree, by use of higher compacting pressure or sintering temperature, is of great effectiveness, especially from the point of view of mechanical properties and fatique endurance. Practical implications: the obtained results demonstrate the benefits of contact infiltration and of reactive sintering techniques to sinter stainless steels components having higher density and better mechanical and corrosion resistance properties than the traditional compositions, compacted at high pressure and sintered at elevated temperature. Originality/value: very promising results have been also obtained with a modified composition able to allow reactive sintering process.

2

Analysis of Densification Process and Structure of PM Al-Mg-Si-Cu-Fe and Al-Zn-Mg-Cu-Sn Alloys

80%

Bidulský R. , Bidulská J. , Actis Grande M.

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tom Vol. 59, iss. 1

17--23

EN

The paper is focused on the role of the pressing pressure on the densification behaviour of PM aluminium alloys. Commercially aluminium based powders Al-Mg-Si-Cu-Fe and Al-Zn-Mg-Cu-Sn were used as materials to be investigated. The apparent density of the powder mixes was determined according to MPIF St. 04. A set of cylinder test specimen 55x10x10 mm3 was uniaxially pressed in a floating hardened steel die. Compaction pressures ranged from 50 MPa up to 700 MPa. Considering the densification of metal powders in uniaxial compaction, quantification of aluminium compaction behaviour was performed. The compressibility behaviour was evaluated, considering the effect on specimens, as well as on their microstructure. The development of compressibility values with pressing pressure enables to characterize the effect of particles geometry and matrix plasticity on the compaction process.

PL

Przedmiotem pracy jest wpływ ciśnienia prasowania na zagęszczanie proszków stopów aluminium. Materiałem badanym były komercyjne proszki aluminium Al-Mg-Si-Cu-Fe I Al-Zn-Mg-Cu-Sn. Gęstość pozorna mieszanek proszków określono według MPIF St.04. Cylindryczne próbki 55x10x10 mm3 ściskane były jednokierunkowo w samonastawnej matrycy z hartowanej stali. Nacisk wahał się od 50 MPa do 700 MPa. Biorąc pod uwagę zagęszczenie proszków metali w trakcie prasowania jednoosiowego, przeprowadzono kwantyfikacje zagęszczania aluminium. Oceniono zachowanie ściśliwości biorąc pod uwagę wpływ na próbki, jak również na ich mikrostrukturę. Zestawienie wartości ściśliwości z ciśnieniem prasowania pozwala scharakteryzować wpływ geometrii cząstek i plastyczności matrycy na proces prasowania.

3

Corrosion resistance of sintered duplex stainless steel evaluated by electrochemical method

80%

Dobrzański L. A. , Brytan Z. , Actis Grande M. , Rosso M.

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tom Vol. 17, nr 1-2

317--320

EN

Purpose: Purpose of this paper was to examine the corrosion resistance of duplex stainless steels using electrochemical methods in 1M NaCl solution. The influence of powder mixes preparation and cooling cycle after sintering on corrosion properties was evaluated. Design/methodology/approach: In presented study duplex stainless steels were obtained through powder metallurgy starting from austenitic, martensitic base powders by controlled addition of alloying elements. In the studies behind the preparation of mixes, Schaffler’s diagram was taken into consideration. Prepared mixes have been compacted at 800 MPa and sintered in a vacuum furnace with argon backfilling at 1260°C for 1h. After sintering two different cooling cycles were applied: rapid cooling with an average cooling rate of 245°C/min and slow cooling of 5°C/min in argon atmosphere. Findings: According to achieved results, it was affirmed that applied sintering method as well as powder mixes preparation allows for manufacturing the sintered duplex steels with good corrosion properties. Corrosion resistance of sintered stainless steels is strictly connected with the density and the pore morphology present in the microstructure too. The highest resistance to pitting corrosion was achieved for composition with approximate balance of ferrite and austenite in the microstructure. Research limitations/implications: According to the powders characteristic, the applied fast cooling rate seems to be a good compromise for corrosion properties and microstructures, nevertheless further tests should be carried out in order to examine different cooling rates and sintering temperatures. Originality/value: The use of elemental powders added to a stainless steel base showed its potentialities, in terms of fair compressibility and final sintered density. In addition a good structural homogeneity and first of all corrosion resistance was achieved, also working with cycles possible for industries.

4

The challenge of PM tool steels for the innovation

80%

Rosso M. , Ugues D. , Actis Grande M.

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tom Vol. 18, nr 1-2

175--178

EN

Purpose: The economical impacts and complexity of tool steels justify the lot of efforts for their development, processing and application. In particular the main goal is the attainment of isotropic microstructures characterised by homogeneous distribution of fine carbide particles and segregation free. The paper offers a review of the Powder Metallurgy tool steels currently manufactured, their properties are discussed with particular regard to their main application and attained performances. Design/methodology/approach: Powder Metallurgy is the way to make the goal, its alloying flexibility allows the production of new tool steels that cannot be made by conventional processes, because of segregation and related hot workability problems. Findings: In practice, through the Powder Metallurgy route it is possible to achieve the highest levels of properties, specifically related to toughness, mechanical behaviour, wear and corrosion resistances of the produced alloys. Research limitations/implications: The use of Powder Metallurgy route allows, through the HIP consolidation from tiny powder particles, to facilitate the production of tool alloy grades able to reach very high performances. Moreover the application of coatings can determin e further advantages. Practical implications: When using thin coatings, like PVD deposited layers, the PM steels more uniformly distributed and fine carbide structure was found to give a clear improvement in the interface quality of the relative coated systems. Conversely, the less uniform traditional steels carbide distribution resulted in a less continuous contact between the substrate and the coating. Originality/value: The paper demonstrate the superior value and perfomances of PM tool steels and their better adaptability to PVD coatings. In particular, cold working, plastics and high speed applications are the main interested and advantageously affected by the uniqueness of PM tool steels. Some comparison between equivalent traditional and PM tool steel grades are presented.

5

The influence of sintering time on the properties of PM duplex stainless steel

80%

Brytan Z. , Dobrzański L. A. , Actis Grande M. , Rosso M.

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2009

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tom Vol. 37, nr 2

387-396

EN

Purpose: The purpose of this paper is to analyse the effect of sintering time on the pore morphology, microstructural changes, tensile properties and corrosion resistance of vacuum sintered duplex stainless steel. Design/methodology/approach: In presented study PM duplex stainless steels were obtained through mixing base ferritic stainless steel powder with controlled addition of elemental alloying powders and then sintered in a vacuum furnace with argon backfilling at 1250°C for different time periods. Produced materials were studied by LOM/SEM metallography and the pore morphology was characterized. The mechanical properties were studied in tensile, hardness and Charpy impact tests. The corrosion resistance was evaluated by means of salt spray test and immersion in sulfuric acid. Findings: Prolongation of sintering time influenced on increase of density thus on the mechanical properties and microstructure balance. Practical implications: Mechanical properties of obtained PM duplex stainless steels are very promising, especially with the aim of extending their field of possible applications. Originality/value: The possibility of obtaining balanced austenitic-ferritic microstructure of stainless steel using elemental powders added to a stainless steel base powder. The vacuum sintering of such powder mixture results in good microstructural homogeneity.

6

Structural analysis of composite powders obtained from recycled material

80%

Suśniak M. , Karwan-Baczewska J. , Dutkiewicz J. , Actis Grande M.

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tom Vol. 33, nr 2

86--89

EN

In presented paper a technology of production of a composite powder from recycled aluminum alloy (AlSi5Cu2) chips using Powder Metallurgy (PM) has been investigated. Mechanical alloying technique was used to mill the blended powder (AlSi5Cu2 + 10 wt % SiC) under argon atmosphere in a high-energy ball mill. After milling the structure of powders mixtures has been investigated using scanning electron microscopy (SEM) and light optical microscopy (LOM). The structural investigations show that homogeneous distribution of SiC reinforcement in the matrix was obtained due to mechanical alloying technique for 20÷40 h. Light microscope observations showed that particle size of obtained composite powder decreased from 200 to about 3 μm. Mechanical properties of the powder were evaluated using microhardness measurements. The microhardness of 40-hour milled powder (AlSi5Cu2 + 10 wt % SiC) attains 350 HV0.025. The influence of the time of mechanical alloying on the selected properties and the structure of composite powders were discussed in detail.

PL

W artykule przedstawiono metodę otrzymywania proszku kompozytowego z wiórów stopu aluminium AlSi5Cu2 z dodatkiem 10% mas. SiC, wykorzystując technologię metalurgii proszków. Mechaniczną syntezę przeprowadzono w wysokoenergetycznym młynie kulowym w atmosferze argonu. Analizę strukturalną wytworzonego proszków wykonano za pomocą mikroskopu świetlnego oraz skaningowego mikroskopu elektronowego. Badania metalograficzne potwierdziły, że proces mechanicznej syntezy prowadzony od 20 do 40 godzin umożliwił uzyskanie proszku kompozytowego o jednorodnym rozkładzie SiC. Jak wykazały badania, podczas mielenia następuje zmniejszenie wielkości cząstek z 200 do 3 μm. Właściwości mechaniczne proszku zbadano poprzez pomiar mikrotwardości. Mikrotwardość proszku mielonego przez 40 godzin zwiększa się do 350 HV0,025. Określono również wpływ czasu mielenia na wybrane właściwości i strukturę wytworzonego proszku.

7

Characteristic of vacuum sintered stainless steels

80%

Brytan Z. , Dobrzański L. A. , Actis Grande M. , Rosso M.

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tom Vol. 33, nr 2

126-134

EN

Purpose: In the present study duplex stainless steels were sintered in vacuum. using rapid cooling form the mixture of prealloyed and alloying element powders The purpose of this paper was to describe the obtained microstructures after sintering as well as the main mechanical properties of sintered stainless steels. Design/methodology/approach: In presented work duplex stainless steels were obtained through powder metallurgy starting from austenitic 316L or ferritic 410L prealloyed stainless steels powders by controlled addition of alloying elements powder. Prepared mixes were sintered in a vacuum furnace in 1250°C for 1h. After sintering rapid cooling (6°C/s) using nitrogen under pressure was applied. Sintered compositions were subjected to structural examinations by scanning and optical microscopy and EDS analysis as well as X-ray analysis. Mechanical properties were studied through tensile tests and Charpy impact test. Findings: It was demonstrated that austenitic-ferritic microstructures with regular arrangement of both phases and absence of precipitates can be obtained with properly designed powder mix composition as well as sintering cycle with rapid cooling rate. Obtained sintered duplex stainless steels shows good mechanical properties which depends on phases ratio in the microstructure and elements partitioning (Cr/Ni) between phases. Research limitations/implications: Basing on alloys characteristics applied cooling rate and powder mix composition seems to be a good compromise to obtain balanced sintered duplex stainless steel microstructures. Practical implications: Mechanical properties of obtained sintered duplex stainless steels structures are rather promising, especially with the aim of extending their field of possible applications. Originality/value: The utilization of vacuum sintering process with rapid cooling after sintering combined with use of elemental powders added to a stainless steel base powder shows its advantages in terms of good microstructural homogeneity.

8

Identification of the critical pore sizes in sintered and ecaped aluminium 6XXX alloy

71%

Bidulská J. , Kvačkaj T. , Pokorný I. , Bidulský R. , Actis Grande M.

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tom Vol. 58, iss. 2

371--375

EN

The main aim of this paper is to investigate, by means of comparison of experimental studies and mathematical models, the evolution of porosity as consequence of pressing, sintering and ECAPping an aluminium based powder (6xxx). After applying the compacting pressure, specimens were dewaxed in a ventilated furnace at 400º for 60 min. Sintering was carried out in a vacuum furnace at 610ºC for 30 min. The specimens were then ECAPed for 1 pass. The 2-dimensional quantitative image analysis was carried out by means of SEM and OM for the evaluation of the aforementioned characteristics. Results show the effect of processing parameters on the fracture/microstructure behaviour of the studied aluminium PM alloy. Quantitative image analysis, as well as fractographic interpretation and microstructure identification of weak sites in the studied aluminium PM alloy, provide a reliable and reproducible statistical procedure for the identification of the critical pore sizes.

PL

Głównym celem pracy jest badanie zmian porowatości podczas prasowania, spiekania i wyciskania przez kanał katowy proszku na bazie aluminium (Ai-Mg-Si-Cu-Fe) za pomocą eksperymentu i symulacji numerycznych. Po przyłożeniu ciśnienia podczas zagęszczania usuwano lepiszcze z próbek w piecu w temperaturze 400ºC przez 60 minut. Spiekanie prowadzono w piecu próżniowym w temperaturze 610ºC przez 30 min. Próbki następnie były wyciskane przez kanał kątowy w jednym przejściu. Dwuwymiarowa ilościową analizę obrazu przeprowadzono za pomocą skaningowej mikroskopii elektronowej i mikroskopii optycznej w celu oceny wyżej wymienionych właściwości. Wyniki opisują wpływ parametrów procesu na pękanie/ mikrostrukturę badanego proszku stopu aluminium. Ilościowa analiza obrazu, jak równiez mikrostruktury w badanym stopie proszku aluminium zapewniają wiarygodne i statystycznie powtarzalne procedury dla identyfikacji miejsc inicjacji pękania.

9

Structure investigation of ball milled composite powder based on AlSi5Cu2 alloy chips modified by SiC particles

71%

Suśniak M. , Karwan-Baczewska J. , Dutkiewicz J. , Actis Grande M. , Rosso M.

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tom Vol. 58, iss. 2

437--441

EN

The paper is focused on the processing of aluminum alloy chips using powder metallurgy. Chips obtained from recycled AlSi5Cu2 alloy were ball milled with the addition of silicon carbide powder with an average size of 2μm. Mechanical alloying process was employed to obtain homogeneous composite powder. The effect of processing time (0 - 40h) on the homogeneity of the system was evaluated, as well as a detailed study of the microstructure of AlSi5Cu2 aluminum chips and SiC particles during MA was carried out. Addition of silicon carbide (10, 20wt%) to recycled aluminium chips and application of MA lead to fragmentation of the homogeneous composite powder down to particle size of about 3μm and spheroidization. The addition of hard SiC particles caused reinforcement and reduced the milling time. Higher content of silicon carbide and longer processing time allowed to obtain AlSi5Cu2/SiC powders with microhardness ~500HV0,025. The results of MA were investigated with SEM, EDS, LOM, XRD and showed that relatively homogeneous distribution of SiC reinforcements in the matrix as well as grain refinement of aluminum solid solution down to 50nm can be obtained after 40h of processing.

PL

W artykule przedstawiono metodę otrzymywania proszku kompozytowego na osnowie wiór stopu aluminium AlSi5Cu2 pochodzących z recyklingu z dodatkiem węglika krzemu (SiC-α, 2μm). Określono wpływ czasu mielenia oraz dodatku SiC na mikrostrukture i właściwości proszku kompozytowego.Dodatek SiC (10, 20%mas) do wiór stopu aluminium i zastosowanie mechanicznej syntezy pozwala na otrzymanie jednorodnego i drobnoziarnistego proszku o wielkości 3μm i kształcie zbliżonym do sferycznego. Dodatek twardych cząstek SiC powoduje umocnienie proszku oraz skrócenie czasu mielenia. Dodatek SiC i zastosowanie 40h mielenia pozwala otrzymać cząstki proszku o mikrotwardości około 500 HV0,025. Badania proszku kompozytowego przeprowadzone na mikroskopie optycznym, SEM oraz TEM potwierdziły jednorodne rozmieszczenie cząstek SiC w osnowie oraz zmniejszenie wielkości ziarna do 50nm po 40 godzinach procesu.

10

Characterization of Microstructural and Mechanical Properties after Cold Rolling of an Electro-Sinter-Forged Cu-Sn Alloy

57%

Gobber F. S. , Bidulská J. , Fais A. , Franchini F. , Bidulský R. , Kvačkaj T. , Actis Grande M. , Gobber F. S. , Bidulská J. , Fais A. , Franchini F. , Bidulský R. , Kvačkaj T. , Actis Grande M.

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