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"Pada makalah ini dibahas karakteristik lapisan WC-Co hasil proses thermal spray dengan teknik HVOF (High Velocity Oxy-Fuel) yang akan diaplikasikan pada pada nosel roket RX-10Q guna menggantikan pelapis grafit masif yang berat. Untuk itu, dilakukan studi pengaruh kekasaran permukaan terhadap kekuatan lekat dan struktur mikro lapisan.Hasil yang diperoleh menunjukkan bahwa variasi tekanan proses penyemprotan (grit blasting) menyebabkan variasi kekasaran permukaan, dimana semakin besar tekanan yang diberikan, semakin kasar permukaan yang diperoleh. Namun, kekuatan kohesi lapisan dan kekerasan lapisan WC-Co tidak dipengaruhi oleh kekasaran permukaan tersebut. Hasil penelitianjuga menunjukkan bahwa tanpa proses persiapan permukaan, lapisan WC-Co thermal spray tidak dapat melekat dengan baik pada logam dasarnya. Analisa struktur mikro lapisan WC-Co menggunakan mikroskop optik dan Scanning Electron Microscope (SEM) menunjukkan bahwa lapisan WC-Co relatifpadat dengan komposisi bervariasi pada daerah berbeda. Terdapat indikasi terjadinya difusi W pada daerah antar-fasa yang berkontribusi pada tingginya kekuatan lekat lapisan.

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This research investigated the characteristics of HVOF (High Velocity Oxy-Fuel) thermal spray WC-Co coating to be applied on the nozzle of RX-100 rocket. In particular, it studied the effects of surface preparation on the mechanical properties and microstructures of the coating.

The results showed that the grit blasting pressure directly influences the surface roughness of the substrate, in -which the greater the pressure, the higher the surface roughness. However, the cohesive strength and hardness of the coating are not affected by the surface roughness. This research also showed that without grit blasting, the WC-Co coating can not be applied on the substrate. Microstructural analysis of the WC-Co coating showed that this coating is relatively dense with variety in chemical content on different area. An indication of the diffusion of Win the interfacial area was found, which is thought to contribute to the high strength of the coating."

"Dengan semakin meningkatnya perkembangan teknologi, tentunya dibutuhkan pula komponen alat produksi pada industri yang mampu menahan kondisi operasi agresif yang mengakibatkan kegagalan material seperti keausan, korosi dan oksidasi temperatur tinggi. Salah satu metode pelapisan material untuk menangani dan mencegah kegagalan tersebut adalah Thermal Spray. Pada penelitian ini, material JIS G 3132 SPHT-2 dan ASTM A213 - T91 diberi perlakuan grit blasting dengan variasi tekanan 2 bar, 3 bar, 4 bar dan 5 bar untuk mendapatkan kekasaran permukaan yang berbeda. Lalu material diperlakukan proses pelapisan dengan metode pelapisan High Velocity Oxygen Fuel. Karakterisasi hasil pelapisan difokuskan pada struktur mikro, morfologi lapisan yang terbentuk, jumlah porositas, distribusi kekerasan dan laju keausan lapisan. Penambahan tekanan grit blasting menghasilkan kekasaran permukaan substrat yang meningkat. Hasil pelapisan menghasilkan struktur mikro yang bertumpuk atau lamel dengan porositas dibawah 2%, dan kekerasan yang dihasilkan sebesar 872 HV. Namun, tidak terdapat pengaruh kekasaran permukaan terhadap laju keausan maupun kekerasan yang diperoleh.

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As technology develops, industries require production component that can withstand agressive operating condition that leads to failure, such as wear, corrosion and high temperature oxidation. Thermal spray is a method to handle and prevent failures of material. In this study, substrate was roughened with grit blasting pressure variation of 2 bar, 3 bar, 4 bar and 5 bar to get the varied surface roughness. Material used was subject to be coated with High Velocity Oxygen Fuel thermal spraying. Characterization of coating deposits focused on microstructure, morphology of the coating, porosity, hardness distribution and wear rate. With the increasing of grit blast pressure, results in a more rough surface. Coating results in a lamellae structure with porosity percentage under 2% and coating hardness to 872 HV. But, there is no direct effect of the surface roughness to the wear rate nor the hardness.

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"[Penelitian ini bertujuan untuk mengetahui pengaruh kekasaran, proses phosphating, serta ketebalan adhesive bonding terhadap ketahanan delaminasi komposit laminat. Variasi kekasaran substrat, yaitu pada rentang 5-8 μm dan 10-13 μm, variasi terhadap proses phosphating, yaitu ada yang melalui proses phosphating dan ada yang tidak, serta variasi ketebalan adhesive baik primer ataupun topcoat dengan rentang 1-5 μm, 6-10 μm, serta 11-15 μm. Pembentukan komposit laminat ini dilakukan melalui proses transfer moulding pada suhu 160 C selama 450 detik. Komposit laminat yang sudah terbentuk kemudian diuji peel-off untuk mengetahui kekuatan delaminasinya lalu dikarakterisasi dengan SEM-EDX. Hasil menunjukan bahwa kekasaran permukaan, lapisan zinc phosphate, serta ketebalan adhesive bonding mempengaruhi ketahanan delaminasi komposit laminat yang diinterpretasikan dengan kekuatan ikat antarlapisan dan visual delaminasi. Kekasaran optimum terjadi pada rentang 10-13 μm dengan kekuatan ikat 179,68 N dan visual delaminasi R-R sebanyak 35%. Adanya lapisan zinc phosphate memberikan nilai kekuatan ikat optimum sebesar 157,38 N dan visual delaminasi R-R sebanyak 50%. Ketebalan adhesive primer optimum terjadi pada rentang 1-5 μm dengan kekuatan ikat 163,35 N dan visual delaminasi R-R sebanyak 50%. Ketebalan adhesive topcoat optimum terjadi pada rentang 6-10 μm dengan kekuatan ikat sebesar 154,65 N dan visual delaminasi R-R sebanyak 41,6%.;This study aims to determine the effect of roughness, phosphating process, and the thickness of the adhesive bonding into delamination resistance of laminate composite. Variation of the substrate roughness are 5-8 μm and 10-13 μm. Some substrates are coated by zinc phosphate and other substrate are uncoated. Variations of the thickness of adhesive primer and adhesive topcoat are in a range of 1-5 μm, 6-10 μm, and 11-15 μm. The process of forming the laminate composite occurs through transfer molding process at 1600C in 450 seconds. Laminate composite that has been formed then tested by peel-off test to determine the strength of delamination. Visual of delamination was characterized by SEM-EDX. The results showed that the optimum surface roughness occurs in the range of 10-13 μm with bonding strength 179.68 N and 35% of R-R visual. The coated substrate has a higher bonding strength compared to uncoated substrate, which is 157.38 N and 50% of R-R visual. The optimum thickness of adhesive primer occurs in the range of 1-5 μm with bonding strength is 163.35 N and 50% of R-R visual. While the optimum thickness of adhesive topcoat occurs in the range of 6-10 μm with a bonding strength is 154.65 N and 41,6% of R-R visual;This study aims to determine the effect of roughness, phosphating process, and the thickness of the adhesive bonding into delamination resistance of laminate composite. Variation of the substrate roughness are 5-8 μm and 10-13 μm. Some substrates are coated by zinc phosphate and other substrate are uncoated. Variations of the thickness of adhesive primer and adhesive topcoat are in a range of 1-5 μm, 6-10 μm, and 11-15 μm. The process of forming the laminate composite occurs through transfer molding process at 1600C in 450 seconds. Laminate composite that has been formed then tested by peel-off test to determine the strength of delamination. Visual of delamination was characterized by SEM-EDX. The results showed that the optimum surface roughness occurs in the range of 10-13 μm with bonding strength 179.68 N and 35% of R-R visual. The coated substrate has a higher bonding strength compared to uncoated substrate, which is 157.38 N and 50% of R-R visual. The optimum thickness of adhesive primer occurs in the range of 1-5 μm with bonding strength is 163.35 N and 50% of R-R visual. While the optimum thickness of adhesive topcoat occurs in the range of 6-10 μm with a bonding strength is 154.65 N and 41,6% of R-R visual, This study aims to determine the effect of roughness, phosphating process, and the thickness of the adhesive bonding into delamination resistance of laminate composite. Variation of the substrate roughness are 5-8 μm and 10-13 μm. Some substrates are coated by zinc phosphate and other substrate are uncoated. Variations of the thickness of adhesive primer and adhesive topcoat are in a range of 1-5 μm, 6-10 μm, and 11-15 μm. The process of forming the laminate composite occurs through transfer molding process at 1600C in 450 seconds. Laminate composite that has been formed then tested by peel-off test to determine the strength of delamination. Visual of delamination was characterized by SEM-EDX. The results showed that the optimum surface roughness occurs in the range of 10-13 μm with bonding strength 179.68 N and 35% of R-R visual. The coated substrate has a higher bonding strength compared to uncoated substrate, which is 157.38 N and 50% of R-R visual. The optimum thickness of adhesive primer occurs in the range of 1-5 μm with bonding strength is 163.35 N and 50% of R-R visual. While the optimum thickness of adhesive topcoat occurs in the range of 6-10 μm with a bonding strength is 154.65 N and 41,6% of R-R visual]"

"Kondisi operasi serta masalah umum yang dihadapi pada material cetakan penempaan dan ekstrusi seperti keausan, korosi, oksidasi temperatur tinggi dan kelelahan fatik berakibat pada penurunan produktifitas akibat kegagalan dari alat kerja sehingga perlu adanya perbaikan maupun penggantian. Semprot logam nyala api oksi-asetilen dianggap sebagai cara yang efektif dalam menurunkan laju keausan permukaan material. Pada penelitian ini, baja perkakas H13 dilakukan pemanasan awal dengan variasi suhu 200°C, 300°C dan 400°C. Lalu material dilakukan dua proses pelapisan yang berbeda yaitu pelapisan WC dan pelapisan WC didahului dengan nikel bond coat. Karakterisasi permukaan baja difokuskan pada struktur mikro, distribusi kekerasan, keausan permukaan, tingkat porositas dan kekasaran lapisan. Hasil ditemukan bahwa pelapisan WC sebagai lapisan atas dengan metode semprot logam nyala api oksi-asetilen dapat meningkatkan kekerasan mikro permukaan baja H13 dari 500 HV hingga mencapai kekerasan 1717 HV. Selain itu nilai laju keausan menurun dari 0,455 mm3/min menjadi 0,070 mm3/min. Pelapisan nikel sebagai bond coat dapat menurunkan sensitivitas kerentanan terhadap pembentukan retak mikro pada daerah antar muka antara lapisan dengan substrat. Peningkatan suhu pemanasan awal pada substrat baja H13 dapat menurunkan tingkat persentase porositas pada lapisan semprot logam nyala api dan meningkatkan nilai kekasaran permukaan Ra pada hasil proses pelapisan.

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Operating conditions and problems that commonly occur in forging and extrusion mold material such as wear, corrosion, high temperature oxidation and thermal fatigue resulting in a decrease of productivity due to the failure, so it is necessary to repair or replacement. Oxy-acetylene thermal spray is considered as an effective way to reduce wear rate of the surface material. In this study, substrate was subjected to preheating variation of 200°C, 300°C and 400°C. Subsequently the material was conducted in 2 different coating processes: WC coating and WC+Ni coating where nickel as a bond coat. The characterization focused on the microstructure, hardness distribution, wear rate, porosity and roughness of the coating.

It was found that WC coating as a top coat gives higher surface hardness from 500 HV up to 1717 HV. Moreover, the value of the wear rate decreased from 0.455 mm3/min into 0.070 mm3/min. Nickel as a bond coat reduce susceptibility to micro cracks formation in the area of the interface between the coating and substrate. Preheat on H13 steel substrate can reduce the percentage level of porosity in thermal spray coating and increase surface coating roughness (Ra) "