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"Korosi dan erosi rentan terjadi pada boiler yang beroperasi pada suhu tinggi, terlebih pada boiler biomassa dengan kandugan alkali klorida yang bersifat korosif. Studi ini dilakukan untuk mengetahui performa dari material terhadap ketahanan korosi dan erosi suhu tinggi di lingkungan biomassa. Peningkatan performa material dilakukan dengan melapiskan material Cr3C2-NiCr pada substrat baja karbon rendah A516. Teknik pelapisan menggunakan teknik pelapisan flame spray dan high velocity oxy fuel (HVOF). Pengujian untuk mengetahui ketahanan korosi sampel menggunakan metode uji korosi uap garam NaCl:55%KCl suhu 600 °C selama 100 jam. Pengujian erosi dilakukan pada suhu ruang dengan sudut 90° dan kecepatan erodent 32 m/s. Analisis morfologi serbuk pelapis maupun lapisan pelapis menggunakan FE-SEM dan mikroskop optik, analisis fasa yang terbentuk menggunakan XRD, ukuran partikel serbuk pelapis menggunakan PSA, sedangkan pengujian mekanik dilakukan menggunakan karakterisasi kekerasan permukaan dan pull-off test. Teknik pelapisan flame spray menghasilkan lapisan dengan porositas lebih dari 3%, sedangkan pelapisan dengan teknik HVOF menghasilkan lapisan dengan porositas kurang dari 3%. Sehingga lapisan dengan teknik HVOF memiliki ketahanan korosi dan erosi yang lebih baik dibanding lapisan dengan teknik flame spray

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Corrosion and erosion are prone when boilers operate at high temperatures. Moreover, in the biomass boiler with the alkali chlorides contain corrosive substance. In this present study, materials were investigated in order to understand the corrosion and erosion resistance in the biomass environment. In order to increase the performance of the material, coating technologies were applied for Cr3C2-NiCr on carbon steel A516 substrate. Flame spray and high velocity oxy fuel (HVOF) techniques were used in this study. The corrosion test was conducted using the NaCl:55%KCl salt vapor corrosion method at 600 °C for 100 hours. Meanwhile, an erosion test was conducted at impinging angle of 90 °C with an erodent velocity of 32 m/s. Morphologies for powder coatings and coatings were analyzed using an optical microscope and FE-SEM. Phase identification was observed using XRD. PSA was used to investigate powder particle size. Meanwhile, the mechanical properties of materials were characterized using surface hardness and pull off test. The flame spray technique exhibited a coating with a porosity value of more than 3%, whereas the HVOF technique showed a coating porosity value of less than 3%. This condition caused coatings that used the HVOF technique to have better corrosion and erosion performance than flame spray technique."

"ABSTRAK

Thermal spray sering diaplikasikan pada leading edge bilah turbin uap untuk meningkatkan ketahanan abrasi. Stellite adalah salah satu material yang sering digunakan dikarenakan ketahanannya yang baik terhadap aus. Penelitian ini bertujuan untuk mengkomparasi properti metode flame spray, plasma spray, dan HVOF dalam mendeposisikan lapisan Stellite ke bilah turbin baja tahan karat martensitik 410. Hasil lapisan plasma spray dan HVOF menunjukkan deposisi lapisan yang rata sedangkan flame spray tidak. Ketiga proses thermal spray memenuhi spesifikasi kuat lekat minimum manufaktur. Rata-rata kuat lekat dan kekerasan tertinggi didapat dari proses HVOF dengan nilai masing-masing 33,1 MPa dan 719 HV. Berdasarkan standar deviasi kuat lekat dan kekerasan, proses HVOF memiliki hasil lapisan paling homogen. Kekerasan substrat di bawah antarmuka pasca proses pelapisan flame spray, plasma spray, dan HVOF masing-masing naik sebesar 236%, 56%, dan 65% dari spesifikasi substrat. Lapisan HVOF memiliki tampilan penampang yang paling baik. Persentase porositas, diameter porositas, dan rata-rata panjang unbonding terkecil didapat pada proses HVOF dengan nilai masing-masing 0,2%, 7,2 μm, dan 31%. Struktur mikro lapisan pasca pengetsaan menghasilkan fasa-fasa yang berhubungan dengan masukan panas. Struktur dendritik terbentuk pada lapisan proses flame spray dan plasma spray pasca pengetsaan, namun tidak pada proses HVOF. Oksida dan karbida kobalt maupun krom mungkin terbentuk pada lapisan.

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ABSTRACT

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Thermal spray is often applied on steam turbine blade leading edge to increase abrasion resistance. Stellite is one of the commonly used material as it is known to wear protection against abrasion, oxidation, and corrosion at elevated temperature. Thermal spray method generally used in industry are flame spray, plasma spray, and HVOF. This research is intended to compare properties of those methods in depositing Stellite coating on 410 martensitic stainless steel turbine blade. Plasma spray and HVOF coating show even deposition while flame spray coating not. Those three coatings meet manufacture minimum bond strength requirement. On the flame spray process, higher preheat temperature resulted in higher bond strength. Preheat temperature variation relatively not affect coating hardness. Highest average bond strength and hardness are got by HVOF process with a value of 4.799 psi (33,1 MPa) and 719 HV respectively. According to bond strength and hardness standard deviation, the HVOF process gives the most homogeneous coating. Substrate hardness just below the coating interface after flame spray, plasma spray, and HVOF process are raised by 236%, 56%, and 65% each from the specification. HVOF coating has the best cross section compared to others with little splat and porosity. Flame spray coating has the most significant and highest amount of porosity.  In terms of percentage and size, HVOF gives the best result with a value of 0,2% and 7,2 μm respectively. The smallest coating interface unbonding is got by the HVOF process, with an average of 31%. Flame spray, plasma spray, and HVOF coating microstructure after etching show phases related to heat input during application. The dendritic structure is observed on flame spray and plasma spray coating after etching but not on HVOF process. Oxides like Cr₂O₃, CoCr₂O₄, CoO, and carbides like CoC, Cr₇C₃, Co₆W₆C, or Cr₂₃C₆ probably formed in the coating based on EDS result. Moreover, chemical composition result also indicates the formation of silicon oxide on coating and iron oxide at the coating interface. 

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