scholarly journals Microstructure and Mechanical Properties of Vacuum Plasma Sprayed HfC, TiC, and HfC/TiC Ultra-High-Temperature Ceramic Coatings

Materials ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 124
Author(s):  
Ho Seok Kim ◽  
Bo Ram Kang ◽  
Seong Man Choi
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Single Layer ◽  
Ceramic Coatings ◽  
Hafnium Carbide ◽  
Vacuum Plasma Spraying ◽  
Vacuum Plasma ◽  
Coating Layers ◽  
Hardness Values ◽  
Ultra High Temperature

To improve the oxidation resistance of carbon composites at high temperatures, hafnium carbide (HfC) and titanium carbide (TiC) ultra-high-temperature ceramic coatings were deposited using vacuum plasma spraying. Single-layer HfC and TiC coatings and multilayer HfC/TiC coatings were fabricated and compared. The microstructure and composition of the fabricated coatings were analyzed using field-emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The coating thicknesses of the HfC and TiC single-layer coatings were 165 µm and 140 µm, respectively, while the thicknesses of the HfC and TiC layers in the HfC/TiC multi-layer coating were 40 µm and 50 µm, respectively. No oxides were observed in any of the coating layers. The porosity was analyzed from cross-sectional images of the coating layers obtained using optical microscopy. Five random areas for each coating layer specimen were analyzed, and average porosity values of approximately 16.8% for the HfC coating and 22.5% for the TiC coating were determined. Furthermore, the mechanical properties of the coating layers were investigated by measuring the hardness of the cross section and surface roughness. The hardness values of the HfC and TiC coatings were 1650.7 HV and 753.6 HV, respectively. The hardness values of the HfC and TiC layers in the multilayer sample were 1563.5 HV and 1059.2 HV, respectively. The roughness values were 5.71 µm for the HfC coating, 4.30 µm for the TiC coating, and 3.32 µm for the HfC/TiC coating.

Effects of heat treatments on oxidation resistance and mechanical properties of ultra high temperature ceramic coatings

2008 ◽  
Vol 202 (18) ◽  
pp. 4394-4398 ◽  
Author(s):  
Mario Tului ◽  
Stefano Lionetti ◽  
Giovanni Pulci ◽  
Elviro Rocca ◽  
Teodoro Valente ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Oxidation Resistance ◽  
Ceramic Coatings ◽  
Heat Treatments ◽  
Ultra High Temperature

Mechanical Properties of Overaluminized MCrAlY Coatings at Room Temperature

2005 ◽  
Vol 127 (4) ◽  
pp. 807-813 ◽  
Author(s):  
Yoshiyasu Itoh ◽  
Masahiro Saitoh
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Volume Fraction ◽  
Bend Strength ◽  
Vacuum Plasma Spraying ◽  
Temperature Oxidation ◽  
Vacuum Plasma ◽  
Mcraly Coatings ◽  
Aluminum Compounds ◽  
Plasma Sprayed

The objective of this study is to compare the mechanical properties of overaluminized MCrAlY coatings sprayed by a vacuum plasma spraying process for the protection against high-temperature corrosion and oxidation in the field of gas turbine components. Recently, the overaluminized MCrAlY coatings are used for improving further the high-temperature oxidation resistance. However, the mechanical properties of aluminized MCrAlY coatings, which have an important effect on coating lives, have not been clarified. Five kind of freestanding MCrAlY specimens (CoCrAlY, CoNiCrAlY, CoNiCrAlY+Ta, NiCrAlY, NiCoCrAlY) were machined from the thick vacuum plasma sprayed (VPS) coatings. And, the heat-treated MCrAlY specimens (1393 K, 2 h, argon cooled and 1116 K, 24 h, argon cooled) and the overaluminized specimens (Al-Cr-Al2O3-NH4Cl pack, 1173–1273 K, 10 h) after the heat-treatment were used. The experimental results suggested that the volume fraction of precipitated aluminum compounds in the VPS MCrAlY coatings and the residual stress induced by the overaluminizing treatment had important effects on the mechanical properties. The Vickers hardness and Young’s modulus of the overaluminized MCrAlY coatings showed higher values in comparison with the VPS MCrAlY coatings. There was a tendency that the bend strength of overaluminized VPS MCrAlY coatings decreased by the aluminizing treatment and also with increasing volume fraction of precipitated aluminum compounds in the VPS MCrAlY coatings. It was also confirmed that the bend strength of aluminized layers themselves was reduced with increasing volume fraction of precipitated aluminum compounds in the VPS MCrAlY coatings. These tendencies were caused by the enrichment of brittle precipitates, such as NiAl and/or CoAl intermetallic compounds.

Cracking at the fold in double layer coated paper: the influence of latex and starch composition

TAPPI Journal ◽  
2019 ◽  
Vol 18 (2) ◽  
pp. 93-99
Author(s):  
SEYYED MOHAMMAD HASHEMI NAJAFI ◽  
DOUGLAS BOUSFIELD, ◽  
MEHDI TAJVIDI
Keyword(s):  
Mechanical Properties ◽  
Double Layer ◽  
Starch Content ◽  
Single Layer ◽  
Double Layers ◽  
Coated Paper ◽  
Coated Papers ◽  
Coating Layers ◽  
Scanned Images ◽  
Packaging Paper

Cracking at the fold of publication and packaging paper grades is a serious problem that can lead to rejection of product. Recent work has revealed some basic mechanisms and the influence of various parameters on the extent of crack area, but no studies are reported using coating layers with known mechanical properties, especially for double-coated systems. In this study, coating layers with different and known mechanical properties were used to characterize crack formation during folding. The coating formulations were applied on two different basis weight papers, and the coated papers were folded. The binder systems in these formulations were different combinations of a styrene-butadiene latex and mixtures of latex and starch for two different pigment volume concentrations (PVC). Both types of papers were coated with single and double layers. The folded area was scanned with a high-resolution scanner while the samples were kept at their folded angle. The scanned images were analyzed within a constant area. The crack areas were reported for different types of papers, binder system and PVC values. As PVC, starch content, and paper basis weight increased, the crack area increased. Double layer coated papers with high PVC and high starch content at the top layer had more cracks in comparison with a single layer coated paper, but when the PVC of the top layer was low, cracking area decreased. No measurable cracking was observed when the top layer was formulated with a 100% latex layer.

Effect of Transition Metal Silicides on Microstructure and Mechanical Properties of Ultra-High Temperature Ceramics

2013 ◽  
pp. 125-179 ◽  
Author(s):  
Laura Silvestroni ◽  
Diletta Sciti
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Melting Point ◽  
Leading Edge ◽  
High Melting ◽  
High Melting Point ◽  
Ultra High Temperature Ceramics ◽  
Sintering Additives ◽  
Self Diffusion ◽  
Ultra High Temperature

The IV and V group transition metals borides, carbides, and nitrides are widely known as ultra-high temperature ceramics (UHTCs), owing to their high melting point above 2500°C. These ceramics possess outstanding physical and engineering properties, such as high hardness and strength, low electrical resistivity and good chemical inertness which make them suitable structural materials for applications under high heat fluxes. Potential applications include aerospace manufacturing; for example sharp leading edge parts on hypersonic atmospheric re-entry vehicles, rocket nozzles, and scramjet components, where operating temperatures can exceed 3000°C. The extremely high melting point and the low self-diffusion coefficient make these ceramics very difficult to sinter to full density: temperatures above 2000°C and the application of pressure are necessary conditions. However these processing parameters lead to coarse microstructures, with mean grain size of the order of 20 µm and trapped porosity, all features which prevent the achievement of the full potential of the thermo-mechanical properties of UHTCs. Several activities have been performed in order to decrease the severity of the processing conditions of UHTCs introducing sintering additives, such as metals, nitrides, carbides or silicides. In general the addition of such secondary phases does decrease the sintering temperature, but some additives have some drawbacks, especially during use at high temperature, owing to their softening and the following loss of integrity of the material. In this chapter, composites based on borides and carbides of Zr, Hf and Ta were produced with addition of MoSi2 or TaSi2. These silicides were selected as sintering aids owing to their high melting point (>2100°C), their ductility above 1000°C and their capability to increase the oxidation resistance. The microstructure of fully dense hot pressed UHTCs containing 15 vol% of MoSi2 or TaSi2, was characterized by x-ray diffraction, scanning, and transmission electron microscopy. Based on microstructural features detected by TEM, thermodynamical calculations, and the available phase diagrams, a densification mechanism for these composites is proposed. The mechanical properties, namely hardness, fracture toughness, Young’s modulus and flexural strength at room and high temperature, were measured and compared to the properties of other ultra-high temperature ceramics produced with other sintering additives. Further, the microstructural findings were used to furnish possible explanations for the excellent high temperature performances of these composites.

Microstructure and Mechanical Properties of SiC Whisker-Reinforced ZrB2 Ultra-High Temperature Ceramic

2008 ◽  
Vol 368-372 ◽  
pp. 1730-1732 ◽  
Author(s):  
Ping Hu ◽  
Xing Hong Zhang ◽  
Jie Cai Han ◽  
Song He Meng ◽  
Bao Lin Wang
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
High Temperature ◽  
Flexural Strength ◽  
Hot Pressing ◽  
Room Temperature ◽  
Pressing Temperature ◽  
Sintering Time ◽  
Microstructure And Mechanical Properties ◽  
Ultra High Temperature

SiC whisker-reinforced ZrB2 matrix ultra-high temperature ceramic were prepared at 2000°C for 1 h under 30MPa by hot pressing and the effects of whisker on flexural strength and fracture toughness of the composites was examined. The flexural strength and fracture toughness are 510±25MPa and 4.05±0.20MPa⋅m1/2 at room temperature, respectively. Comparing with the SiC particles-reinforced ZrB2 ceramic, no significant increase in both strength and toughness was observed. The microstructure of the composite showed that the SiC whisker was destroyed because the SiC whisker degraded due to rapid atom diffusivity at high temperature. The results suggested that some related parameters such as the lower hot-pressing temperature, a short sintering time should be controlled in order to obtain SiC whiskerreinforced ZrB2 composite with high properties.

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