scholarly journals Microstructures and Oxidation Behaviors of Silicide Coated Nb Alloys by Halide Activated Pack Cementation Process

2020 ◽  
Vol 58 (8) ◽  
pp. 507-514
Author(s):  
Wonchul Yang ◽  
Choong-Heui Chung ◽  
Sangyeob Lee ◽  
Kyeong Ho Baek ◽  
Youngmoo Kim ◽  
...  
Keyword(s):  
Oxidation Resistance ◽  
Coating Layer ◽  
Pack Cementation ◽  
Powder Mixtures ◽  
Arc Melting ◽  
Static Oxidation ◽  
Coating Layers ◽  
Pack Cementation Process ◽  
Coating Layer Thickness ◽  
Oxidation Behaviors

In this study, we tried to improve the oxidation resistance of Nb-12Si (wt%) alloys at 1200 °C or higher through pack cementation coatings. Nb-12Si (wt%) alloys were prepared by arc-melting under Ar atmosphere. When the alloys were coated using pack powder mixtures composed of Si, Al2O3 and NaF, two silicide layers composed of NbSi2 and Nb5Si3 phases were successfully produced on the substrate. The Si-pack coatings were performed with various heat treatment temperatures and time conditions. The microstructures and thickness changes of the coating layers were analyzed to determine the growth behaviors of the coating layer. The growth constant of 8.4 10–9 cm2/sec was obtained with a diffusion growth mode. In addition, in order to examine the resistance of the Si-pack coated alloys, isothermal static oxidation tests were performed at 1200 °C and higher temperatures. As a result, the oxidation resistance of the alloys was determined by protecting the surface of the alloys with silicide oxide layers formed by the silicide coatings. The uncoated specimens exhibited an abnormal weight increase due to the formation of Nb oxide. The coated specimen showed excellent oxidation resistance at 1200 °C for up to 12 hrs, while the previous reports on the same alloy verified oxidation resistance only up to 1100 °C. It appears that the excellent oxidation resistance is closely related to the NbSi2 coating layer thickness. The oxidation behaviors of the coating layers after the oxidation tests were discussed in terms of microstructural and phase analyses.

Investigation of the SHS Process Initiation in Base Mixture during HFC-Heating and the Combustion Rate Dependence on Various Factors

2021 ◽  
Vol 1031 ◽  
pp. 67-74
Author(s):  
Alexey V. Ishkov ◽  
Vladimir N. Malikov ◽  
Alexander Shegolev
Keyword(s):  
Combustion Rate ◽  
Coating Layer ◽  
Thin Layers ◽  
Powder Materials ◽  
Charge Composition ◽  
Powder Mixtures ◽  
Factors Influencing ◽  
Main Factors ◽  
Ignition And Combustion ◽  
Coating Layer Thickness

The paper describes the researches of the SHS process initiation in samples of powder mixtures of reagents intended for steel parts hardening with an excess of Al or B2O3 by a heat source. Mixtures of reagents with different weight ratios of components were used as samples. Thereat, the initiation of SHS process in thin layers was conducted with a coating layer thickness of no more than 6 mm for all tested compositions. The dependences of the combustion rate on various factors including particle size of powder materials and charge composition have been obtained. The main factors influencing the dependences of initiation (ignition) and combustion rate are established, and the degree of influence of these factors on the dependences is estimated. The obtained results made it possible to correct the composition of the base mixture reasonably in order to achieve the required combustion rate.

Oxidation resistance of SIC–AlN ceramics coated by oxidation-assisted-pack cementation process

2011 ◽  
Vol 31 (3) ◽  
pp. 369-376 ◽  
Author(s):  
Giuseppe Magnani ◽  
Francesco Antolini ◽  
Leandro Beaulardi ◽  
Alida Brentari ◽  
Emiliano Burresi
Keyword(s):  
Oxidation Resistance ◽  
Pack Cementation ◽  
Pack Cementation Process

scholarly journals Microstructural investigation of the coatings prepared by simultaneous aluminizing and siliconizing process on γ-TiAl

2019 ◽  
Vol 55 (2) ◽  
pp. 217-225
Author(s):  
S. Nouri ◽  
M. Azadeh
Keyword(s):  
Powder Mixture ◽  
Pack Cementation ◽  
Chemical Compositions ◽  
Powder Mixtures ◽  
Microstructural Investigation ◽  
Diffusion Coatings ◽  
Sequential Mechanism ◽  
First Time ◽  
Pack Cementation Process ◽  
Segregated Structure

In this research, formation of aluminide/silicide diffusion coatings on ?-TiAl[Ti-48Al-2Nb?2Cr (at.%)] alloy using gasphase diffusion pack cementation process has been investigated. The application of powder mixtures with various chemical compositions in the pack cementation process performed at 1000oC for 6 hours in order to achieve simultaneous diffusion of Al and Si, showed that the composition of the powder mixture could have a significant effect on the structure and thickness of the aluminide/silicide coatings. The identification and analysis of aluminide/silicide microstructures formed as a result of simultaneous diffusion of Al and Si, which was comprehensively and qualitatively done for the first time in this study, showed that the sequential mechanism is dominant in the formation of the above-mentioned coatings. Furthermore, Kirkendall phenomenon and volumetric changes caused by the formation of Ti5Si3 and Ti5Si4, were considered as the two dominant mechanisms in the formation of porous segregated structure in these coatings. In this study, the effect of decreasing the activity of Si, through two approaches of reducing the amount of Si in the powder mixture and using Al- 20wt.%Si alloyed powder instead of pure Al and Si depositing elements, on the microstructural modification coatings was investigated. The results showed that reducing the Si activity at the surface of the coating and, consequently, reducing the flux of active silicon atoms (JSi), has a significant effect on the formation of coating with an ideal structure.

Formation and Oxidation Resistance of NbSi2 Coatings on Niobium by Pack Cementation

2007 ◽  
Vol 280-283 ◽  
pp. 907-910 ◽  
Author(s):  
Ming Li ◽  
Lixin Song ◽  
Jun Le ◽  
Xiao Wei Zhang ◽  
Bao Gen Pei ◽  
...  
Keyword(s):  
Phase Composition ◽  
Oxidation Resistance ◽  
Single Phase ◽  
Element Distribution ◽  
Pack Cementation ◽  
Cross Sectional ◽  
Pure Niobium ◽  
Before And After ◽  
Pack Cementation Process

NbSi2 coatings were formed on niobium by halide-activated pack cementation process. The as-coated niobium samples were oxidized in air up to 1723 K by thermogravimetry method. The surface and cross-sectional morphology, phase composition and element distribution of the NbSi2 coatings before and after oxidation were characterized by SEM, XRD and EPMA. The results show that the as-formed coatings consist of single phase of hexagonal NbSi2 and the oxidation resistance of pure niobium can be greatly improved by pack siliconizing.

Effect of Pack Al Content on Growth Kinetics at 650 °C of Ni2Al3 Coating Layer on Nickel-Electroplated Creep Resistant Ferritic Steels

2011 ◽  
Vol 399-401 ◽  
pp. 2008-2012
Author(s):  
D.J. Wu ◽  
W.H. Hua ◽  
Z.D. Xiang ◽  
C.Y. Zhu
Keyword(s):  
Layer Thickness ◽  
Growth Kinetics ◽  
Coating Layer ◽  
Ferritic Steels ◽  
Minimum Level ◽  
Powder Mixtures ◽  
Al Content ◽  
Nickel Electroplating ◽  
Kinetics Of ◽  
Pack Cementation Process

The hybrid Ni2Al3/Ni coating was formed on creep resistant ferritic steels by firstly nickel electroplating and then partially aluminising the Ni layer at 650 °C by pack cementation process using powder mixtures of Al, AlCl3and Al2O3. The effect of pack Al content (W) on growth kinetics of the outer Ni2Al3layer of the coating was investigated by varying it from 2 to 10 wt% whilst keeping the pack AlCl3content constant at 2 wt% and aluminising conditions at 650°C/4h. It was revealed that, once W was above a minimum level, the growth of the outer Ni2Al3layer thickness depended linearly on W1/2. The possible reasons for such growth kinetics were discussed.

MODIFIED SiC-MoSi2 OXIDATION PROTECTIVE COATING FOR SiC-COATED CARBON/CARBON COMPOSITES THROUGH INFILTRATING LIQUID Si

2011 ◽  
Vol 18 (03n04) ◽  
pp. 109-114 ◽  
Author(s):  
ZHENG-ZHONG ZHANG ◽  
HE-JUN LI ◽  
CHAO MA ◽  
QIAN-GANG FU ◽  
YU-LEI ZHANG ◽  
...  
Keyword(s):  
Phase Composition ◽  
Mass Loss ◽  
Oxidation Resistance ◽  
Protective Coating ◽  
Pack Cementation ◽  
Carbon Composites ◽  
Test Results ◽  
Oxidation Test ◽  
Coated Carbon ◽  
Pack Cementation Process

To improve the oxidation resistance of the SiC-MoSi2 coating prepared by two-step pack cementation, a liquid Si infiltrating method was adopted to modify it. The phase composition and microstructure of the coatings were analyzed by XRD and SEM. The results show that the size and number of the cracks in the modified coating decreased evidently after infiltrating Si . The oxidation test results in air at 1773 K show that the mass loss of the SiC-MoSi2 coating coated carbon/carbon (C/C) composites was up to 1.18% after oxidation for 206 h, while that of the modified coating coated C/C composites was only 0.77% after oxidation for 460 h. The reason is that the cracks formed in the pack cementation process were partly sealed and there were no penetrable cracks in the modified coating. Therefore, there were no direct channels for the oxygen to diffuse into the C/C substrate.

Oxidation Behaviors of DO3 Type Fe3Si Based Intermetallics at 900°C

2010 ◽  
Vol 146-147 ◽  
pp. 1904-1910
Author(s):  
Qi Zhou ◽  
Jian Gang Jia ◽  
Hong Shun Zhao ◽  
Xin Min Zhang
Keyword(s):  
Oxidation Resistance ◽  
Oxidation Product ◽  
Oxidation Reaction ◽  
Protective Oxide ◽  
Kinetics Of Oxidation ◽  
Good Oxidation Resistance ◽  
Arc Melting ◽  
Protective Oxide Film ◽  
Kinetics Of ◽  
Oxidation Behaviors

In the present work, intermetallics Fe3Si and Fe3 (Si1-xAlx) (x=0.33, 0.67, 0.80) produced by arc melting, were evaluated regarding the oxidation at 900°C in air. The test preformed was the isothermal and cyclic oxidation. The microstructures of oxide films were analyzed by XRD, SEM, EDS, EPMA. The result showed that the four kinds of intermetallics had good oxidation resistance at 900°C.The addition of Al element can increase the oxidation resistance of Fe3Si based intermetallics. The oxidation kinetics of the four intermetallics follows the rule of the parabola. The main oxidation product of Fe3Si is SiO2.The kinetics of oxidation reaction is mainly controlled by Si diffusion. The oxidation product of three Al alloying Fe3Si based intermetallics is Al oxide. Al moves outward from the substrate to form a protective oxide film which restrained the diffusion of Si and Fe outward.

Measurement of mechanical properties of multilayer waterborne coatings on wood by nanoindentation

Holzforschung ◽  
2019 ◽  
Vol 73 (9) ◽  
pp. 871-877 ◽  
Author(s):  
Yan Wu ◽  
Jiamin Wu ◽  
Siqun Wang ◽  
Xinhao Feng ◽  
Hong Chen ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Cell Walls ◽  
Coating Layer ◽  
Intact Cell ◽  
Bonding Mechanism ◽  
Thickness Direction ◽  
Waterborne Coatings ◽  
Coating Layers ◽  
Wood Surfaces ◽  
Coating Layer Thickness

AbstractWaterborne coatings are widely used for environmental protection. However, they lead to many defects and lower the mechanical properties when applied to wood surfaces. To address this challenge, the effects of multilayer waterborne polycrylic coatings on the mechanical properties of southern pine cell walls were investigated by nanoindentation. The experimental results indicated that the coating layers significantly reduced the elastic modulus (Er) and hardness (H) values than the wood cell walls. TheErandHvalues measured along the coating layer thickness direction increased significantly as the distance of the indents to the wood surface decreased. Intact cell walls adjacent to or away from the coating layers had higherErandHvalues than partial ones. This study will also be useful in helping to understand the bonding mechanism at the interface between coatings and wood cell walls.

Sign in / Sign up

Export Citation Format

Share Document