Papers by Author: Simo Pekka Hannula

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Authors: Simo Pekka Hannula, Erja Turunen, Jari Keskinen, Tommi Varis, Teppo Fält, Tom E. Gustafsson, Roman Nowak
Abstract: HVOF thermal spraying has been developed to deposit dense Al2O3-coatings for improved protective properties. As compared to generally used plasma sprayed coatings HVOF coatings can be prepared much denser and thus are better suited for applications where protective properties of the coating are needed. In this paper we describe the development of HVOF spraying technologies for nanocrystalline Al2O3- and Al2O3-Ni-coatings. The microstructure and the mechanical properties of these novel coatings are reported and compared to a conventionally processed Al2O3-coating.
539
Authors: Juha Larismaa, Toni Honkanen, Yan Ling Ge, Outi Söderberg, Michael Friman, Simo Pekka Hannula
Abstract: Antibacterial silver can be used against such micro-organisms as bacteria and molds. When Ag nanoparticles are attached to an inorganic carrier, e.g., silica long-term antimicrobial functionality can be gained. Such Ag-SiO2 particles are potential for water purification or bactericidal applications. In this work, submicron sized silica particles doped with Ag were prepared by the modified Stöber method. The as-prepared powder was air-dried and annealed for 75 minutes at 573, 673, 773, 873, 973, 1073, 1173, or 1273 K in air. The powders were studied by DSC/TGA, XRD, SEM, TEM and UV-vis methods. The as-prepared powder consisted of round silica particles having size around several hundred nanometers. XRD and SEM studies confirmed that the powder consisted of metallic silver nanoparticles on the submicron silica surface after annealing at 873 K or higher. According to the SEM study the silver particles had an average particle size between 19-400 nm depending on the annealing temperature. DSC was used to determine the phase transformation temperatures. After annealing the Ag-SiO2 powder at 873 K the TEM study suggested that the silver had crystalline structure. The XRD studies confirmed that silver appeared as a FCC crystal structure. The UV-vis measurements of Ag-SiO2 powder annealed at and below 773 K showed a steady increase in absorption with decreasing wavelength without absorption peaks. Annealing at 873 K and above resulted in a strong peak in between 404 nm and 416 nm. This peak can be attributed to the surface plasmon resonance of silver nanoparticles.
449
Authors: Seung Ho Kim, Sung Hun Cho, Simo Pekka Hannula, Soo Wohn Lee
Abstract: Solid lubricants were suited for the applications of high temperature parts. Recently, researches for self-lubricating ceramic matrix composites using solid lubricants, such as MoS2, WS2, h-BN, and graphite etc., became active. This work is to use the spark plasma sintering (SPS) technique in order to make self-lubricating Al2O3/15wt% ZrO2 nanocomposites with higher mechanical properties. To optimize the self-lubricating Al2O3/15wt% ZrO2 nanocomposite systems were added with different solid lubricants (CaF2, BaF2, MoS2, WS2, h-BN, and graphite). The coefficient of friction of CaF2, h-BN and graphite added composites in steady-state at room temperature are below 0.3.
404
Authors: Seung Ho Kim, M. Erkin Cura, Outi Söderberg, Simo Pekka Hannula, Soo Wohn Lee
Abstract: The coefficient of friction was very important factor for the applications of high temperature parts. In vehicles, the coefficient of friction was decreased due to lubricants as like engine oil etc. Lubricant such as oils is difficult to apply at high temperature. To apply high temperature parts, lubricants were demanded for high temperature stability. This work is to use the pulsed electric current sintering (PECS) technique and the atmospheric plasma spraying (APS) method in order to make self-lubricating Al2O3-15wt% ZrO2-solid lubricant composites. We focused on the coefficient of friction for the fabrication method of self-lubricating Al2O3-15wt% ZrO2-solid lubricant composites. We compared with the coefficient of friction of PECSed and APSed composites. The surface roughness of PECSed Al2O3-15wt% ZrO2-solid lubricant composites were 0.06 ~ 0.31 μm of Ra and 10.16 ~ 33.12 μm of Ry. In the case of APSed Al2O3-15wt% ZrO2-solid lubricant composites, as-coated samples were 6.56 ~ 11.42 μm of Ra and 59.68 ~ 81.79 μm of Ry, and polished samples were 1.12 ~ 3.70 μm of Ra and 11.66 ~ 32.22 μm of Ry. The coefficient of friction of PECSed and APSed Al2O3-15wt% ZrO2-solid lubricant composites were 0.19 ~ 0.49 and 0.41 ~ 0.61, respectively.
231
Authors: Erja Turunen, Tommi Varis, Jari Keskinen, Teppo Fält, Simo Pekka Hannula
Abstract: Special nanoreinforced ceramic composite coatings were produced. Dense nanostructured alumina and chromia coatings alloyed with various nanofraction elements such as Ni, NiO, ZrO2 and SiC were manufactured by HV2000 HVOF spraying. As a result coatings with nearly 100% improvements relative fracture toughness, were produced.
1240
Authors: Ilkka Aaltio, Outi Söderberg, Yan Ling Ge, Simo Pekka Hannula
Abstract: Martensitic 10M Ni-Mn-Ga single crystals are usually applied in the magnetomechanical actuators. Their behavior in the long-term cycling and the factors influencing upon are thus important to know. There are several publications concerning this. However, consistent statistical data is still missing to large extent. In this report we review and analyze the data available in the literature. In conclusion it can be stated that 10M Ni-Mn-Ga single crystals survive well in long-term actuation (millions of cycles) when the frequency of twin variant reorientation is not exceeding 250 Hz, and the strain used in actuation is below 3 %. There are several factors influencing the long-term behavior and these are discussed in more details in this work.
203
Authors: Simo Pekka Hannula, Teppo Fält, Erja Turunen, Timo Manninen
114
Authors: Erja Turunen, Tommi Varis, Tom E. Gustafsson, Jari Keskinen, Pertti Lintunen, Teppo Fält, Roman Nowak, Simo Pekka Hannula
Abstract: Special mechanical properties have widely been demonstrated with bulk nanocrystalline materials. An increasing effort has been made to transfer such improvements also into thermal sprayed ceramic coatings. This paper focuses on such efforts in alumina-based ceramic coatings. The optimization of process conditions and effect of different process parameters on the mechanical performance of high velocity oxy-fuel (HVOF) sprayed ceramic coatings is discussed.
545
Authors: Simo Pekka Hannula, P. Lintula, Pertti Lintunen, Tomi Lindroos
1971
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