Rochim Suratman

Effect of Ti Addition on Oxidation Behavior and Area Specific Resistance of Fe-20Cr Alloys for SOFC Interconnects

In this work, the oxidation behavior of Fe-20wt.%Cr alloys with different titanium contents: 0, 0.5, and 1 wt.% are studied as a function of time in air atmosphere. The samples were isothermally oxidized at 700°C for 24, 48, and 96 h in a box furnace. The area specific resistance of oxides formed at the alloys surface during oxidation is measured by four-point probe methods at 700°C for 24 h. For Ti containing alloys, surface morphology observation by SEM shows that a few of TiO2 particles formed on the top of Cr2O3 scales. Continous TiO2 layer was not formed at the alloys surface after oxidation. XRD analysis on the oxide scales of Fe-20Cr-Ti alloys confirms that Cr2O3 and TiO2 oxide formed on the alloys. Ti addition into the alloys increases the oxidation rates of alloys at the initial stages. Oxidation behavior of Fe-20Cr-0.5Ti and Fe-20Cr-1Ti alloys showed two regimes. The parabolic rate constant, kp (in gr2/cm4s) were 1.57 x 10-13 and 3.08 x 10-13 respectively for initial stage of oxidation then changed to-9 x 10-15 and-3 x 10-14 respectively for the remainder of the test. ASR measurement shows that the presence of Ti in the alloys decreases the electrical resistance up to 60%. Ti addition into Fe-Cr alloys affect the oxide growth rate and increase the conductivity of Cr2O3 scales.

Sifat Tarik Dan Sifat Impak Komposit Polipropilena High Impact Berpenguat Serat Rami Acak Yang Dibuat Dengan Metode Injection Molding

Rami merupakan salah satu jenis serat alam yang banyak tumbuh di Indonesia dan memiliki sifat mekanik yang baik. Hingga saat ini, pemanfaatan rami sebagai material penguat pada komposit polimer berpenguat serat alam telah banyak dipelajari. Namun, penggunaan serat rami sebagai bahan penguat dan polipropilena high impact (PPHI) yang banyak digunakan dalam industri otomotif sebagai matriks dalam komposit untuk aplikasi di bidang otomotif belum banyak dipelajari. Pada penelitian ini dipelajari pengaruh fraksi volume serat rami terhadap sifat tarik dan sifat impak komposit PPHI berpenguat serat rami. Komposit PPHI dibuat dengan menggunakan injection molding pada temperatur 190 0C dengan fraksi volume serat rami sebesar 5%, 10%, dan 15%. Pengujian densitas dan pengujian fraksi volume bahan penyusun diukur dengan mengacu pada ASTM D 792 dan ASTM D 3171. Kekuatan tarik komposit diukur dengan mengacu pada standar ASTM 3039. Harga Impak dari komposit diukur dengan mengacu pada ASTM D 6110-04. Dari penelitian ini dapat disimpulkan bahwa kekuatan tarik komposit tertinggi dimiliki oleh komposit PPHI berpenguat serat rami dengan fraksi volume serat sebesar 10%, yaitu sebesar 18.17 Mpa, lebih tinggi 21% dibandingkan dengan kekuatan tarik PPHI yang tidak diperkuat oleh serat rami. Harga impak komposit tertinggi juga dimiliki oleh komposit PPHI berpenguat serat rami dengan fraksi volume serat 10%, yaitu sebesar 46.39 KJ/m2, lebih tinggi 15.5% dibandingkan dengan PPHI yang tidak diperkuat oleh serat rami.

The Effect of Thermo-mechanical Treatment of Substrate Preparation and Carburizing Temperature on The Morphology and Hardness of Carburizing on Low Carbon Steel

Low carbon steel has a lot of applications in daily life because of its excellent properties. Among its excellent properties are good ductility, toughness, formability, and weldability. For the case of application that requires good wear resistant, carbon steel is not sufficient. For this case it is required to increase the hardness of carbon steel, such as by carburizing method. In this method one factor that affects the carburizing layer is metal substrate condition, i.e grain size. Another factor is temperature that could have significant role on the carburized layer characteristics. Therefore the present works focus in the correlation between degree of reduction of cold rolling and carburizing temperature on the carburized layer characteristic. Thermo-mechanical treatment was applied to the specimen with reduction of 0%, 30%, and 80% by mean of rolling before carburizing process. Carburizing processes were carried out at temperature of 850°C, 900°C, and 950°C. Examinations on carburized specimens were conducted by metallography and micro hardness test. The result showed that the specimen of 80% reduction giving the thickest layer and the hardest surface layer. In addition, at temperature of 900°C, the hardest layer was formed with the hardness at 1003 HV. However, the thickest layer was formed at the temperature of 950°C.

Preparation of Zn-ZrO2 Nanocomposite Coating by DC and Pulsed Current Electrodeposition Technique with Low Current Density

In the present work, Zn-ZrO2 nanocomposite coatings were deposited on the copper substrate through DC and pulse electrodeposition technique with low current density (10 mA/cm2). The effect addition of ZrO2 nanoparticles and pulse current were studied. The surface morphology, microhardness and erosion resistance of Zn-ZrO2 nanocomposite coating were evaluated. The result shows that, with the addition of ZrO2 particles, the surface morphology of Zn-ZrO2 nanocomposite coating was smoother. Phase identification by XRD confirm that Zn layer had been sucessfully deposited. The presence of ZrO2 nanoparticles was not detected. Compared to DC, pulsed current electrodeposition technique showed higher cathodic efficiency, better microhardness and good erosion resistance.

Oxidation Characteristics of Cr2O3-La2O3 and NiAl-La2O3 Coated on Ferritic Stainless Steel by Thermal Spray Method

The present works concerns in evaluating thermal oxidation characteristic of composite coating on ferritic stainless steel at high temperature application. SUS430 ferritic stainless steel was used as the substrate material whereas Cr2O3-La2O3 and NiAl-La2O3 were used as the coating material. Thermal spray has been used as the deposition method, whereas thermal oxidation at temperature of 750°C for 24, 48 and 96 hours has been employed on the coated material in the atmosphere environment. From the weight meausurement before and after thermal oxidation, it was observed insignificant weight losses, whereas this condition is stable for all the applied oxidation period. However weight losses is more on the NiAl-La2O3 as compared with Cr2O3-La2O3 samples, which is due to the morphological characteristic of the former layer as observed by scanning electron microscope (SEM) characterization. From X-ray diffraction (XRD) characterization, it was observed the formation of stable layer Cr2O3 for Cr2O3-La2O3 coated samples, whereas formation of NiO observed for the case of NiAl-La2O3 sample.

Development of HVOF Coating of Hydroxy Apatite on Titanium Alloy with Carbon Nano Tube Intermediate Layer

Hydroxyapatite (HA) is considered as convenient material for the coating of titanium alloy in implant aplication. With the purpose to improve the morphology structure of HAP coating, the present research concerns in studying the effect of carbon nanotube (CNT) intermediate layer on HAP coated of titanium alloy. From SEM characterization, it can be observed that both of HAP coated sample, with and without CNT intermediate layer have porous nodular structure a characteristic of thermal spray coating without any micro-crack. However finer and more irregular structure observed on the sample with CNT intermediate layer, which is confirmed from XRD characterization, that lower degree of crystallinity occur on sample with CNT intermediate layer. After the coating, both of the samples were post annealed at 600 and 700°C for one hour. It was observed that micro-crack observed on the sample without CNT intermediate layer after post annealed at 700°C, while the rest of both samples observed without micro-crack.

Preferred Growth Orientation of Cementite Carbide by Phase-Field Simulation

A morphological evolution of the crystals growth has been investigated using two dimensional (2D) multi-phasefield (MPF) simulations. Cementite carbide growth is taken as an example in the present case, while concern is given in simulating the preferred growth orientation of the carbide. In order to evaluate competitive growth between carbide seeds, variations on carbide seed orientation have been implemented. In the present model, variation of the seed orientations are embedded on the interfacial energy, thereby the anisotropy characteristic of interfacial energy can be obtained. Simulation utilized homogenous grain orientation that less than the preferred growth orientation results insignificant grain growths (first case). In the opposite way, simulation utilized homogenous grains orientation that equal or more then the preferred growth orientation, results in the homogenous significant grain growth (second case). On the other hand, simulation utilized heterogenous grains orientation involving grains in the first and second case, results a competition growth that inhibit and diminish the grains in the first case. It can be concluded that the present simulations works can shows the existence of preferred orientation growth during grain growth phenomena including the growth of cementite carbide phase.

Effect of Cold Rolling Treatment on the Formation of Titanium Oxide Layer on Ti6Al4V Alloys by Thermal-electrochemical Anodizing Processes

The present work concerns on preparing suitable titanium alloy substrate that might induce better characteristic of titanium oxide layer on the substrate. Different degree of cold rolling treatments were applied on Ti6Al4V alloy before thermal-electrochemical anodizing processes. The later processes were performed to produce titanium oxide layer which combines thermal process by heat treatment and followed with electrochemical anodizing process. After thermal heat treatment process, it was observed more homogeneous titanium oxide layer for the samples given cold rolling treatment as compared with sample without the treatment. This condition is believed due to the finer substrate surface after cold rolling treatment as observed from surface roughness measurement. Similar situation was observed after anodizing process that irregular oxidized layer was observed for sample without cold rolling treatment, whereas more homogenous layer was observed for sample with cold rolling treatment. Except for sample without cold rolling treatment, anodizing treatment tends to create finer oxidized layer. Therefore, it can be concluded that cold rolling treatment on titanium substrate before oxidizing process induces the formation of homogeneous oxide layer, whereas additional anodizing process create finer titanium oxide layer.

Oxidation Characteristics of Various Nickel Composite Coated on Ferritic Stainless Steel

The present works concerns in developing alternative interconnect material for solid oxide fuel cell (SOFC) application. For this purpose, ferritic stainless steel is used as the substrate material while various nickel composite layers were coated on the substrate in order to improve its oxidation resistance at SOFC application temperature. Nickel layers were deposited on ferritic stainless steel by high velocity oxy-fuel (HVOF) method. In order to create nickel-oxide layer, the coated samples is then heated at temperature of 950°C for 1 hour, wherease sol-gel coating was performed on the coated samples in order to create nickel manganese oxide spinnel composite layers. All samples were then oxidized at temperature 800°C for 8 hours, in order to evaluate their oxidation characteristics at SOFC service temperature. Before and after oxidation, x-ray diffraction (XRD) and scanning electron microscope (SEM) were performed to all samples. It was observed that coated samples effectively inhibit the formation of chromium oxide that normally occurs on stainless steel surface at SOFC service temperature.

Prospect of Identification of Different Corrosion Product by Near-IR Photography

The present work is a preliminary work on the development of NIR camera photograph as alternative tool for corrosion product identification. Corrosion products were taken from two different carbon steel tubes side, one is from thinning tube side, the other is from normal tube side. From optical microscope data, it was observed that the thinning tube side surface has elongated microstructure while the other has normal microstructure. It was also observed that more stable oxide in the form of hematite formed on the thinning tube side, while the other side has siderite and magnetite as the corrosion product. From NIR camera photograph on the scale of both tubes side, it was obtained significant differences in the digital image number. It is expected that after further comprehensive collecting digital image number data on the various corrosion product as well as thickness layer, NIR camera photograph can be used as an alternative method for corrosion product identification.