A. Molinari

Università degli Studi di Trento, Trient, Trentino-Alto Adige, Italy

Are you A. Molinari?

Claim your profile

Publications (198)142.13 Total impact

  • N. Corsentino · I. Cristofolini · M. Larsson · A. Molinari ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Press and sinter is a near net-shape technology, and its cost effectiveness is strictly related to the geometrical and dimensional precision of the component itself. In this work an analytical model to describe the dimensional variations due to the sintering process of iron components has been proposed and discussed. This model has been developed using experimental data coming from a well designed sampling. The sampling is a set of axisymmetric geometries, rings and cylinders, having different diameters and heights. The different features (diameters and heights) have then been compared with the dimensional variations to study the influence of the geometry on the dimensional variations. Every sample has been measured both in the green state and after the sintering process. The dimensional variations concerning the diameters and the heights have been evaluated. The measuring procedure has been implemented using a coordinate measuring machine. The sintering process has been carried at three different temperatures under the same operating conditions. The anisotropy of the dimensional variations has been studied and described within the proposed model, introducing the anisotropy parameter (K). Basically the parameter K identifies the difference between the dimensional variations occurring in an ideal isotropic volumetric change and the actual anisotropic volumetric variation. The model can describe the difference between the dimensional variations occurring on the compaction plane (diameters) and the dimensional variations occurring along the compaction axis (height). The effect of the geometry and the sintering temperature on the anisotropy of the dimensional variations has been evaluated.

  • Powder Technology 07/2015; 278:323. DOI:10.1016/j.powtec.2015.03.042 · 2.35 Impact Factor
  • G. Cipolloni · M. Pellizzari · A. Molinari · M. Hebda · M. Zadra ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Mechanical milling is a suitable technique to enhance various properties of copper by the severe plastic deformation involved during the process. Contamination from milling media is one of the major problems of mechanical alloying. In this study, the behaviour of copper powder during mechanical milling was investigated in order to minimize iron and chromium contaminations. Hence, three different parameters have been studied to highlight the high influence of ball milling parameters on the final products. The parameters included the type of process control agent (none, toluene or stearic acid), the ball-to-powder weight ratio (33:1 or 10:1) and finally, a change in the milling cycle (interrupted or continuous) in an interactive procedure according to the experimental results. As a result, the best morphology and contamination level combination was observed in powder milled with stearic acid; it was 10:1 for the ball to powder ratio when using a continuous milling cycle. Once the best milling conditions were determined, the resulting samples were exposed to spark plasma sintering (SPS). The sintering parameters were selected based on a previous thermal gravimetrical measurement of the milled powders to avoid residual porosity. The final density of all of the samples is very good, 99%, confirming an effective densification process and sintering activated by severely strain-hardened and nanostructured particles.
    Powder Technology 05/2015; 275. DOI:10.1016/j.powtec.2015.01.063 · 2.35 Impact Factor
  • L. Emanuelli · M. Biesuz · S. Libardi · P. Marconi · A. Molinari ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The influence of the mechanical properties of a diffusion bonded Ni-Cu-Mo sintered steel on the residua! stresses and the plastic deformation promoted by both steel and ceramic shot peening was investigated. While steel shots deform the surface more extensively than ceramic ones, leading to a thicker surface densification, ceramic shots are more effective in terms of maximum compressive residual stresses. The increase in the yield strength of the base material enhances residual stresses and reduces plastic deformation. The strain induced transformation of Ni-rich austenite in martensite causes a slight decrease of tensile elongation and of impact energy in specimens sintered at low temperature.
    La Metallurgia Italiana 03/2015; 107(3):23-28. · 0.23 Impact Factor
  • Source
    Simone Zanzarin · Sven Bengtsson · Alberto Molinari ·
    [Show abstract] [Hide abstract]
    ABSTRACT: High power diode laser with coaxial powder injection was used to deposit single tracks of cobalt alloys with tungsten carbides on to a carbon steel plate in order to study carbide dissolution in the metallic matrix. Two kinds of cobalt alloy powders (Stellite 12 and Stellite 21) having different content of tungsten and carbon were used. Processing parameters were changed to obtain different cladding conditions, and effect of substrate preheating was evaluated too. Carbides dissolution, measured with image analysis and EDXS analysis, increases with the increase in the laser power. A low carbon and the absence of tungsten in the matrix powder promote carbides dissolution. Substrate preheating also leads to a higher dissolution. Matrix microhardness of the Stellite 21 increases with the increase in carbides dissolution, while matrix microhardness of the Stellite 12 does not change. Hardness of the coatings is slightly influenced by the dissolution phenomena.
    02/2015; 27(S2):S29209. DOI:10.2351/1.4906480
  • C. Menapace · G. Cipolloni · A. Molinari ·

    Materials Science Forum 12/2014; 802:483-488. DOI:10.4028/www.scientific.net/MSF.802.483
  • Ibrahim Metinoz · Ilaria Cristofolini · Alberto Molinari ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The dry sliding wear behavior of two sintered and carburized steels with different Ni amounts has been investigated. The microstructure of the two steels comprises martensite, bainite, and the Ni-rich austenite. Under the sliding conditions investigated, wear is either oxidative or adhesive. In both cases, the lower amount of the soft Ni-rich austenite results in a better wear resistance. A design procedure for parts subject to dry sliding wear applications is proposed, based on the maximum acceptable wear depth, in order to evaluate the practical significance of the differences between the two materials.
    Journal of Materials Engineering and Performance 10/2014; 23(10):3630-3639. DOI:10.1007/s11665-014-1135-0 · 1.00 Impact Factor
  • S. Zanzarin · S. Bengtsson · L. Maines · A. Molinari ·
    [Show abstract] [Hide abstract]
    ABSTRACT: High power diode laser with coaxial powder injection was used to deposit single tracks of austenitic stainless steel on to a carbon steel plate, and the influence of heat input and powder density on energetic efficiency of the process, as well as on some geometrical features of the clad and on dilution was investigated. The energetic efficiency, calculated as the energy used to form the clad and the Heat Affected Zone, tends to increase with the powder density, while it decreases on increasing heat input. The combination of a high powder density and a low heat input is expected to optimize the energetic efficiency. In these conditions, the chemical dilution of the clad is minimized whilst aspect ratio is rather low but still acceptable. Moreover, the energy spent for the powder and the substrate can be correlated to the iron contamination of the clad.
    La Metallurgia Italiana 09/2014; 106(9):5-50. · 0.23 Impact Factor
  • Ilaria Cristofolini · Nicolò Corsentino · Alberto Molinari · Mats Larsson ·
    [Show abstract] [Hide abstract]
    ABSTRACT: In the conventional press and sinter process, dimensional change on sintering determines the precision of the final parts, providing that a good dimensional precision of green parts is ensured. Anisotropic dimensional change on sintering may be detrimental to the precision of Powder Metallurgy (PM) parts, and it should be considered in the design step. The effect of material and geometry on the anisotropic dimensional change is studied in this work. Four different iron alloys and five different geometries were considered. Dimensions were measured both on green and on sintered parts and the anisotropy of dimensional change was evaluated and correlated to the material and geometry. The effect of neglecting anisotropy in the design step was investigated, in terms of dimensional tolerances, which can be obtained with different process capabilities. A model to describe the effect of material and geometry on the anisotropic dimensional change is also being developed.
    International Journal of Precision Engineering and Manufacturing 09/2014; 15(9):1865-1873. DOI:10.1007/s12541-014-0540-5 · 1.50 Impact Factor
  • Ibrahim Metinoz · Ilaria Cristofolini · Alberto Molinari ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The dry-sliding wear behavior of two high-density, sinter-hardened, powder metallurgy (PM) steels was found to depend on the formation and stability of a protective oxide layer on the contact surface. The presence of soft nickel-rich austenite in a nickel-alloyed steel prevents the formation of the layer and, therefore, the nickel-free steel shows superior wear resistance. A design procedure for parts subject to dry-sliding wear applications is proposed based on the maximum acceptable wear depth. The influence of sliding conditions on wear depth is calculated and the possibility of improving the performance of parts by varying the material characteristics and part geometry is discussed.
    International Journal of Powder Metallurgy 09/2014; 50(4):43-53. · 0.41 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A conservative approach to predict the contact fatigue behavior of a Powder Metallurgy steel, in the sinter-hardened condition and after shot peening, was proposed. It is based on the assumption that the contact fatigue crack nucleation is anticipated by the local plastic deformation of the material, which occurs when the maximum local stress exceeds the yield strength of the matrix. A model to predict contact fatigue crack nucleation has been proposed and validated by experiments. A local approach is used, based on the characteristics of the largest pores, which promote fatigue crack nucleation, and on the microhardness of the microstructural constituents where they are localized. Shot peening improves the contact fatigue resistance of the sinterhardened steel by 30%.
    Materials Science and Engineering A 09/2014; 614:81–87. DOI:10.1016/j.msea.2014.07.009 · 2.57 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A systematic characterisation of the porosity in the bulk and surface regions of a sintered Cr-Mo low alloy steel was carried out using image analysis. Fractional porosity in the different regions varies, mainly due to the scatter of the maximum pore size. A higher porosity is found in the bulk region and lower porosity in the regions that contact the die surface during compaction. The maximum pore size is larger in the bulk region than in the surface layers. The large pores are more irregular. With increasing green density, both the fractional porosity and maximum pore size decrease. The fraction of load bearing section in the bulk and surface regions was calculated from fractional porosity and the shape factor of the pores and compared in the different regions. The load bearing section fraction and the maximum pore size were used to predict tensile and fatigue resistance for different densities. The data from the characterisation of the bulk images can predict tensile strength. For fatigue, where the crack nucleates in the surface regions, the use of bulk data underestimates the fatigue resistance.
    Materials Characterization 08/2014; 94. DOI:10.1016/j.matchar.2014.05.005 · 1.85 Impact Factor
  • K. Bendo Demetrio · C. Menapace · A. Molinari ·
    [Show abstract] [Hide abstract]
    ABSTRACT: In this work it has been investigated the hot deformation of a 2024 Al alloy obtained by spark plasma sintering of cryomilled powder. This behaviour was compared with the one of a sample produced with atomized powder. Different hot deformation responses were observed since their microstructures are different. In the milled sample grains are nanometric and ultrafine and contain some precipitates. A much higher concentration was observed in the atomized specimen, since this powder is a supersaturated solid solution and SPS causes the whole of the precipitation sequence, resulting in the extensive intragranular precipitation of incoherent particles. The different microstructures lead to a different hot compression behaviour. Milled alloy has a higher flow stress and shows a peculiar stress–strain curve characterized by a sharp peak of the flow stress followed by a rapid decrease. This work softening was correlated to the phenomenon of the dynamic precipitation occurring only in the milled specimen.
    04/2014; 3(2). DOI:10.1166/mat.2014.1166
  • A. Molinari · E. Bisoffi · C. Menapace · J. Torralba ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Dilatometry experiments have been carried out to investigate the shrinkage kinetics on cold isostatic pressed iron specimens in the 550-730 degrees C temperature range, showing that dimensional contraction is much higher than that predictable on the basis of the shrinkage kinetics models, which neglect the effect of the prior cold compaction. The greater shrinkage is due to an enhanced diffusivity which may be attributed to the large density of structural defects accumulated in the powder particles during compaction (structural activity). A time depending effective lattice diffusion coefficient was determined, with an Arrhenius type dependence on temperature.
    Powder Metallurgy 02/2014; 57(1):61-69. DOI:10.1179/1743290113Y.0000000068 · 0.77 Impact Factor
  • Source
    Menapace C. · Zanella C. · Cazzolli M. · Libardi S. · Deflorian F. · Molinari A. ·

    International Journal of Powder Metallurgy 01/2014; 50(3):41-48. · 0.41 Impact Factor
  • S. Diouf · C. Menapace · M. D’Incau · A. Molinari · G. Ischia ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The densification and sintering behaviour of a cryomilled copper powder (grain size of 17±2 nm and dislocation density of 6.26±0. 04×1016 m-2) were investigated and compared to those of an atomised copper powder with the same mean particle size in order to highlight the effect of the nanostructure on spark plasma sintering (SPS). Oxygen and nitrogen contamination of the cryomilled powder gives rise to extensive degassing during SPS up to 400°C. The cryomilled powder is more resistant to plastic deformation than the atomised one, but the huge density of dislocations and grain boundary activates sintering at low temperature. Densification is therefore promoted by deformation in the atomised powder and by sintering shrinkage in the cryomilled one. As a consequence, in the SPS conditions investigated, the atomised specimen is densified but not sintered, while the cryomilled one is effectively sintered and consequently densified.
    Powder Metallurgy 12/2013; 56(5):420-426. DOI:10.1179/1743290113Y.0000000065 · 0.77 Impact Factor
  • Source
    Saliou Diouf · Anna Fedrizzi · Alberto Molinari ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The effect of the surface overheating occurring during spark plasma sintering was investigated by means of a fractographic and microstructural analysis of specimens produced with large copper particles. The overheated layer is quite thick and its microstructure is clearly different from that of the bulk of the particles, comprising coarse columnar grains oriented along the radial direction. Such a microstructure indicates that the temperature at the surface of the particles may effectively overcome the melting point of the material, leading to fast melting and re-solidification.
    Materials Letters 11/2013; 111:17-19. DOI:10.1016/j.matlet.2013.08.056 · 2.49 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effect of the sintering and sinter-hardening temperature on the dimensional and geometrical precision of ring-shaped parts was investigated. The parts were produced with a 3%Cr-0.5%Mo-0.5%C steel, compacted to 6.8 g/cm(3) and sinter/sinter-hardened at 1250A degrees C, 1300A degrees C and 1350A degrees C. The increase in the sintering temperature enhances the fraction of load bearing section and leads to an expected significant improvement of mechanical properties. Dimensional shrinkage increases with the sintering temperature, however, the dimensional and geometrical precision obtained in all the cases is very good even at very high sintering temperature. Dimensional variations are anisotropic, and the effect of anisotropy was estimated by evaluating the lack of precision attained when green parts are designed assuming an isotropic behavior.
    International Journal of Precision Engineering and Manufacturing 10/2013; 14(10):1735-1742. DOI:10.1007/s12541-013-0233-5 · 1.50 Impact Factor
  • Enzo Castellan · Gloria Ischia · Alberto Molinari · Rishi Raj ·
    [Show abstract] [Hide abstract]
    ABSTRACT: We apply an in situ approach, whereby a polymer is incorporated into copper and evolves within the metal into the ceramic phase, to create a dispersion of hard particles in a metal. All constituents for the ceramic phase are contained within the organic polymer. The temperature for this polymer to ceramic conversion lies in the 1073 K to 1273 K (800 °C to 1000 °C) range. The process produces a nanoscale dispersion of the ceramic, which leads to high microhardness that remains unaltered at temperatures up to 1223 K (950 °C) (0.9T M). Apparently, the introduction of the ceramic phase leads to the retention of copper crystallite size of a few hundred nm, despite exposure to heat treatments at these very high temperatures. We call these materials polymer-derived metal-matrix composites.
    Metallurgical and Materials Transactions A 10/2013; 44(10). DOI:10.1007/s11661-013-1835-3 · 1.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Ti–6Al–2Sn–4Zr–6Mo is a a + b titanium alloy that combines the long-term strength at elevated temperature with the hardenability by heat-treatments.In this work the effect of conventional heat treatments on the microstructure is investigated,in relation with the hardness properties ofthe material, by Optical Microscopy (OM),Scanning Electron Microscopy (SEM),Energy Dispersion X-ray Spectroscopy (EDXS) and X-ray diffraction (XRD).According to the Rietveld method the quantitative phase analysis by XRD has been carried out, showing the evolution of the phases with the different heat treatments. Solution- treated samples exhibit a microstructure of a-phase crystals embedded in a matrix of retained- b phase and/or a00 martensite, depending onsolution treatment temperature;the a-phase amount depends on the solution-treatment temperature.The presence ofthe a00 martensite does not lead toa significant hardening ofthe material.The aging treatment induces the transformation ofthe retained- b phase and the martensite in a very fine a + b structure that hardens the alloy. The hardness is related to the amount of the fine(a + b)-phase and a linear dependence on the b-phase amount formed during the solution treatment can be identified.
    Journal of Alloys and Compounds 08/2013; 567:134-140. DOI:10.1016/j.jallcom.2013.03.046 · 3.00 Impact Factor

Publication Stats

2k Citations
142.13 Total Impact Points


  • 1990-2015
    • Università degli Studi di Trento
      • • Department of Industrial Engineering
      • • Departmental Area of Materials Engineering and Industrial Technologies
      Trient, Trentino-Alto Adige, Italy
  • 2011
    • University of Cambridge
      • Department of Materials Science and Metallurgy
      Cambridge, England, United Kingdom
  • 2010
    • Museo delle Scienze, Trento, Italy
      Trient, Trentino-Alto Adige, Italy
  • 2004
    • Università degli studi di Cassino e del Lazio Meridionale
      • Department of Mechanics, Structures, Environment and Territory (DIMSAT)
      Cassino, Latium, Italy