Influences of Y Addition on Mechanical Properties and Oxidation Resistance of CrN Coating

AbstractCr1-xYxN coatings were fabricated by reactive co-sputtering deposition and the Y content was changed by varying the Y target power. The influence of varying amounts of Y addition on the mechanical properties and oxidation resistance of CrN coatings has been studied. The results reveal that Y ions substitute Cr ions in Cr-N lattice forming the solid solution Cr1-xYxN coatings. Y doping has a beneficial effect on the improvements of hardness and adhesion of the coatings. After the oxidation in air at 850°C for 2h, The CrN coating with 1.2 at. % Y addition exhibits superior oxidation resistance than Y-free CrN coating, while over doping of Y produces detrimental effects on oxidation resistance of the coatings

Improved hardness and oxidation resistance for CrAlN hard coatingswith Y addition by magnetron co-sputtering

This study aims to investigate the influence of Y content on microstructure, hardness and oxidation resistance of the quaternary CrAlYN hard coatings. The CrAlYN coatings were deposited by magnetron co-sputtering using Cr50Al50 composite and pure Y targets. The Y content increases from 0 to 2.3at.% with Y target power increasing from 0 to 150W while Cr50Al50 target power keeping constant at 250W. Electron probe microanalysis (EPMA) and X-ray diffraction (XRD) results indicate that Y atoms substitute Cr and/or Al atoms in CrAlN lattice forming the solid solution CrAlYN coatings. The surface and cross-sectional morphologies of the CrAlYN coatings exhibit tapered grains and columnar structure respectively. Moreover, the tapered grain sizes and the column widths decrease with increasing Y content. Nanoindentation result reveals a promoted hardness of the CrAlYN coatings from 16.9±0.8GPa to 24.1±1.0GPa with enhanced Y content from 0 to 2.3at.% due to both of the solid solution strengthening and Hall-Petch effect. The oxidation result demonstrates that the Y content beneficial for the oxidation resistance of the CrAlYN coatings is between 0.3 and 0.7at.%. Excess Y addition (≥1.3at.%) significantly deteriorates the oxidation resistance of the CrAlYN coatings as a result of the formation of porous and non-protective oxide scales. ? 2014 Elsevier B.V

Molecular cloning and expression analysis of hypoxia inducible factor 1α in tongue sole, Cynoglossus semilaevis (Actinopterygii: Pleuronectiformes: Cynoglossidae), subjected to acute hypoxia

Background. Hypoxia-inducible factor-1α (HIF-1α), a subunit of the HIF-1 protein, plays a key role in the regulation of genes involved in hypoxia physiological response. Tongue sole, Cynoglossus semilaevis Günther, 1873, a marine teleost, had been proved to be a hypoxia-tolerant species. In this study, the HIF-1α in tongue sole was cloned and its expression under acute hypoxia was examined to provide further basis for understanding the molecular response of tongue sole under hypoxia. Materials and methods. The full length of HIF-1α cDNA sequence was cloned from the liver of tongue sole by RT-PCR and RACE-PCR method. Then, the expression pattern of tongue sole HIF-1α under acute hypoxic conditions were detected using quantitative real-time PCR method. Results. The open reading frame of tongue sole HIF-1α is 2208 bp, encoding 735 amino acids. The amino acid sequence of tongue sole HIF-1α shared high identities (52.7%–81.8%) with HIF-1α from other vertebrates, and possessed six typical domains of the HIF-1 family (bHLH, PAS-A, PAS-B, PAC, N-TAD, and C-TAD). In adult fish, HIF-1α mRNAs were highly expressed in the liver, moderately in the heart, spleen, kidney, stomach, blood and gills, and low in intestine. Under acute hypoxia stress, expression of HIF-1α mRNAs were significantly up-regulated in many tissues, including the liver, spleen, stomach, blood, heart and gills. Conclusion. Tongue sole HIF-1α possessed the similar sequence length, shared higher identities and clustered well with other known HIF-1α, thus revealing a high degree conservation of HIF-1α during evolution. Tongue sole HIF-1α began to be up-regulated from 5 min to 120 min after hypoxia, indicating that it might play a significant role at the early stage of hypoxia

Influence of niobium addition on microstructure, mechanical properties and oxidation resistance of ZrN coatings

In this study, Zr-Nb-N coatings with 0-3.8 at.% Nb addition were deposited by magnetron co-sputtering deposition. The results reveal that Nb atoms substitute Zr atoms in Zr-N lattice, forming the solid solution structure. All the Zr-Nb-N coatings illustrate a dense columnar structure with the preferred orientation of (200), showing independent of Nb addition. Nanoindentation result reveals a promoted hardness of the Zr-Nb-N coatings from 23.9 ± 0.7 GPa to 28.4 ± 0.5 GPa with enhanced Nb content from 0 to 2.8 at.% due to both the solid solution strengthening and Hall-Petch effect. Scratch tests show that adhesion between substrates and coatings can be improved by Nb addition. After oxidation in air at 600 °C for 2 h, microstructural studies indicate the oxide scales consist of monoclinic-ZrO2 outer layer and tetragonal-ZrO2 inner layer. Moreover, ZrO2 can be stabilized in the tetragonal phase by Nb doping. The Zr-Nb-N coating with 1.3 at.% Nb addition exhibits superior oxidation resistance, while excess Nb addition produces detrimental effects on oxidation resistance

Relationship between tribological properties and oxidation behavior of Ti034Al066N coatings at elevated temperature up to 900C

In this study, Ti0.34Al0.66N coatings were fabricated by arc ion plating (AIP) process on ceramic carbide substrates. The tribological tests were carried out by using a ball-on-disc tribometer with different temperatures from 25°C to 900°C in air. After high-temperature testing, the microstructure, chemical composition, oxidation behavior and mechanical properties were investigated using X-ray diffraction, Auger electron spectroscopy, X-ray photo-electron spectroscopy, scanning electron microscopy and nanoindentation tests. Phase separation and crystallization of oxide layer occurred at 900°C. The decrease of surface hardness and significant improvements on wear resistance were obtained at high temperatures, which were connected to the oxidation behavior of Ti0.34Al0.66N coatings. The results showed that the formation of oxide layer determined the contacting state between the slider and coatings at elevated temperatures, and was responsible for the changes in wear mechanisms. ? 2012 Elsevier B.V