Formation of carbonitride precipitates in hardfacing alloy with niobium addition

Niobium, as the most effective second-phase forming element, was added in the Fe-Crl3-C-N hard- facing alloy to get carbonitride precipitates. Morphology and composition of carbonitride in the hardfacing alloy were studied by optical microscopy, scanning electron microscopy, and electron probe microanalyzer. The ther- modynamics and the effect on the matrix of the formation of carbonitride were also discussed. It was found that niobium carbonitrides are complex Nb（C, N） precipitate distributed on grain boundary and matrix of the hardfacing alloy. Under as-welded condition, primary carbonitride particles were readily precipitated from the hardfacing alloy with large size and morphology as they were formed already during solidification. Under heat treatment condi- tion, a large number of secondary carbonitrides can pre- cipitate out with very fine size and make a great secondary hardening effect on the matrix. As a result, addition of niobium in the hardfacing alloy can prevent the formation of chromium-rich phase on grain boundaries and inter- granular chromium depletion.

THEORETICAL CALCULATION OF SPECIFIC INTERFACIALENERGY OF SEMICOHERENT INTERFACE BETWEEN MICROALLOY CARBONITRIDES AND AUSTENITE

According to the misfitting dislocation theory,a method of theoretical calculation was devel- oped for the specific energy of the semicoherent interface between microalloy carbonitrides and austenite matrix.The calculating formulae were derived and the results were satisfactorily applied on the research works.

Coarsening behavior of MX carbonitrides in type 347H heat-resistant austenitic steel during thermal aging

In this work, the growth kinetics of MX （M - metal, X - C/N） nanoprecipitates in type 347H austenitic steel was systematically studied. To investigate the coarsening behavior and the growth mechanism of MX carbonitrides during long-term aging, experiments were performed at 700, 800, 850, and 900℃ for different periods （1, 24, 70, and 100 h）. The precipitation behavior of carbonitrides in specimens subjected to various aging conditions was explored using carbon replicas and transmission electron microscopy （TEM） observations. The corresponding sizes ofMX carbonitrides were measured. The results demonstrates that MX carbonitrides precipitate in type 347H austenitic steel as Nb（C,N）. The coarsening rate constant is time-independent; however, an increase in aging temperature results in an increase in coarsening rate of Nb（C,N）. The coarsening process was analyzed according to the calculated diffusion activation energy of Nb（C,N）. When the aging temperature was 800-900℃, the mean activation energy was 294 kJ·mol -1, and the coarsening behavior was controlled primarily by the diffusion of Nb atoms.

Effect of electrolyte temperature on the nano-carbonitride layer fabricated by surface nanocrystallization and plasma treatment on a γ-TiAl alloy

The distribution of nano-carbonitrides produced by the treatments of surface nanocrystallization and plasma electrolytic carbonitriding on a γ-TiAl was investigated by means of figure analysis. The skewness and kurtosis of Gaussian shape distribution curves were studied and the effect of electrolyte temperature was determined. The usage of lower temperatures of the electrolyte is more suitable for achieving lower sizes of complex nano-carbonitrides. The surface roughness of treated samples was measured and it was observed that there is an optimum level of electrolyte temperature for surface roughness increase （difference between two measured data）.

Two-dimensional titanium carbonitride MXene as a highly efficient electrocatalyst for hydrogen evolution reaction

In this paper,we report,for the first time,on the electrochemical catalytic activity of 2D titanium carbonitride MXene for hydrogen evolution reaction(HER).According to our study,2D titanium carbonitride exhibited much higher electrocatalytic activity than its carbide analogues,achieving an onset overpotential of 53 mV and Tafel slope of 86 mV dec^(-1),superior to the titanium carbide with onset overpotential of 649 mV and Tafel slope of 303 mV dec^(-1).The obtained onset overpotential for 2D titanium carbonitride is lower than those of all the reported transition metal carbides MXene catalysts without additives,so far.Density functional theory calculations were conducted to further understand the electrochemical performance.The calculation results show that a greater number of occupied states are active for Ti_(3)CNO_(2),revealing free energy for the adsorption of atomic hydrogen closer to 0 than that of Ti_(3)C_(2)O_(2).Both experimental and calculation studies demonstrate the excellent electrocatalytic behavior of titanium carbonitride.The investigation of 2D titanium carbonitride opens up a promising paradigm for the conscious design of high-performance non-precious metal catalyst for hydrogen generation.

Laser-Plasma Deposition of Silicon Carbonitride Films by the HMDS Vapor Gas Flow Activation after a Laser Beam Focus

A new laser-plasma deposition method has been developed for the plasma chemical deposition of hard silicon carbonitride coatings on stainless steel substrates from the hexamethyldisilazane (HMDS) Si2NH(CH3)6 vapor in a high-speed Ar and Ar + 10 vol.% He gas stream at the HMDS gas flow activation after the laser beam focus. The method allows depositing silicon carbonitride coatings at the rate of 0.4 - 1.2 μm·min-1, i.e. ~2 times higher than that at introducing HMDS in the laser beam focus zone. The properties of the prepared coatings have been studied by the methods of IR and Raman spectroscopy, atomic force microscopy, nanoindentation and X-ray diffraction (XRD) analysis. Studying the film structure with the use of XRD showed that the prepared silicon carbonitride coatings are X-ray amorphous. It has been found that the coating deposition rate and the structure of coatings depend on the process parameters: HMDS flow rate and plasma-generating gas (argon or (Ar + He). The method allows depositing SiCN films at a high speed and a hardness of 20 - 22 GPa.

STRAIN-INDUCED ISOTHERMAL PRECIPITATION OF Nb,V AND Ti CARBONITRIDES IN MICROALLOYED STEELS DURING CONTROLLED ROLLING

The strain-induced isothermal precipitation and the law of coarsening of Nb,V and Ti carbonitrides in Nb-steel.V-steel.Nb-V steel and Ti-V-Nb steel have been investigated systematically by means of STEM,EDAX,a new extraction replica technique and the quanti- tative phase analyses method.

CN bond orientation in metal carbonitride endofullerenes：A density functional theory study

The geometric and electronic structures of scandium carbonitride endofullerene Sc3CN@C2n （2n=68, 78, 80, 82, and 84） and Sc（Y）NC@C76 have been systematically investigated to identify the preferred position of internal C and N atoms by density functional theory （DFT） calculations combined with statistical mechanics treatments. The CN bond orientation can generally be inferred from the molecule stability and electronic configuration. It is found that Sc3CN@C2n molecules have the most stable structure with C atom locating at the center of Sc3CN cluster. The CN bond has trivalent form of[CN]3- and connects with adjacent three Sc atoms tightly. However, in Sc（Y）NC@C76 with[NC]-, the N atom always resides in the center of the whole molecule. In addition, the stability of Sc3CN@C2n has been further compared in terms of the organization of the corresponding molecular energy level. The structural differences between Sc3CN@C2n and Sc3NC@C2n are highlighted by their respected infrared spectra.

BEHAVIOR OF FINE V-Ti COMPLEX CARBONITRIDE IN STEEL 09MnVTiN DURING REHEATING

An investigation was carried out of the morphology and microstructure of V-Ti complex carbonitride in steel 09MnVTiN during reheating under analytical electron microscope.The prior V-rich ellipsoid V-Ti complex carbonitride particles are replaced progressively by Ti-rich cubic ones as the reheating temperature elevated from 1050 to 1400℃.The Ti con- tents in the core and border of particles increase from 15 and 6% in hot-rolled specimens into 84 and94% at 1400℃ respectively.

LATTICE PARAMETERS OF COMPLEX CARBONITRIDE CONTAINING Ti,Nb AND V

The lattice constants and chemical composition of Ti,Nb and V precipitates with different particle sizes have been measured hy means of CBED and EDAX.It was obtained that the concentration ratio Of Nb and V,C_(Nb)/C_V,and the lattice constants in the Nb-V steel de- crease with the decrease of the particle size of the precipitates,but there is no regularity for tattice constant of Ti,N b and V precipitate against their particle size in the Ti-V-Nb steel.

Characteristics and stability of oxide+carbonitride in H13 steel at 1250℃

The morphology,size,quantity,and composition of complex oxide+carbonitride in H13 steel held at 1250℃for 5,10,and 15 h were determined.The results show that the ratio and number of complex carbonitrides with cores in H13 steel are gradually increased when holding at 1250℃compared with those in the original H13 steel,and the core size increases.There are one or more oxide cores in(Ti_(x),V_(1-x))(Cy,N_(1-y)),including xCaO·zAl_(2)O_(3),xCaO·yMgO·zAl_(2)O_(3),and CaO after holding at 1250℃,in addition to MgO·Al_(2)O_(3)and Al_(2)O_(3)in the original steel.The equilibrium temperature for(Ti_(x),V_(1-x))(Cy,N_(1-y))precipitation at the solidification front and decomposition in the solid state was theoretically analyzed,which was affected by the x value and the product of Ti and N contents in H13 steel.Meanwhile,the composition of(Ti_(x),V_(1-x))(Cy,N_(1-y))is influenced by the oxide cores.It is convinced that(Ti_(x),V_(1-x))(Cy,N_(1-y))with oxide cores has a higher stability,especially for oxides with a high Al_(2)O_(3)content.Heat treatment at high temperature facilitates a more reasonable analysis of oxide+carbonitride,and the generation mechanism of oxide+carbonitride was discussed.

Fabrication of multi-anionic high-entropy carbonitride ultra-high-temperature ceramics by a green and low-cost process with excellent mechanical properties

As a new category of ultra-high-temperature ceramics(UHTCs),multi-anionic high-entropy(HE)carbonitride UHTCs are expected to have better comprehensive performance than conventional UHTCs.However,how to realize the green and low-cost synthesis of high-quality multi-anionic HE carbonitride UHTC powders and prepare bulk ceramics with excellent mechanical properties still faces great challenges.In this work,a green,low-cost,and controllable preparation process of(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C,N_(1-x) powders is achieved by sol-gel combined with the carbothermal reduction/nitridation method for the first time.The as-synthesized(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C_(x)N_(1-x) powders possess high compositional uniformity and controllable particle size.In addition,the obtained bulk ceramics prepared at 1800℃exhibit superior fracture toughness(Kic)of 5.39±0.16 MPa·m^(1/2) and high nanohardnesof 35.75±1.23 GPa,lastic modulus(E)of 566.70±8.68 GPa,and flexural strength of 487±41 MPa.This study provides a feasible strategy for preparing the high-performance HE carbonitride ceramics in a more environmentally friendly and economical manner.

Thermodynamic model for precipitation of carbonitrides in microalloyed steels and its application in Ti-V-C-N system

Based on mass balance and solubility product equations, a thermodynamic model enabling the calcula- tion of equilibrium carbonitride composition and relative amounts as a function of steel composition and tem- perature was developed, which provides a method to es- timate the carbonitride complete dissolution temperature for different steel compositions. Actual carbonitride pre- cipitation behavior was further verified in Ti-V-C-N microalloyed steel system. The model suggests that for higher IV] and [Ti] dissolved in steels, it is available to decrease the addition of C and N during alloy composi- tion design. The resultant longer fatigue life of the modified steel could be attributed to the more [V] and [Ti] dissolved in the matrix, inducing finer dispersion of carbonitrides. Therefore, this model is proved to be effective in determining better chemical composition for high-performance steels, leading to possible reductions in the cost of production and improvements in the combined mechanical properties of the steels.

Precipitation and Solid Solution of Titanium Carbonitride Inclusions in Hypereutectoid Tire Cord Steel

The properties of titanium carbonitride Ti（CxN1-x） inclusions precipitated during solidification of tire cord steels and the thermodynamic conditions for their decomposition and solid solution during billet heating were investigated using a thermodynamics method. The solid solution of Ti（CxN1-x） inclusions during high-temperature heating was also studied experimentally. The results revealed that： （1） the higher the content of carbon in the tire cord steel is, the greater the value of .r in the Ti（CxN1-x） inclusions is; （2） the higher the content of carbon in the tire cord steel is, the earlier the Ti（CxN1-x） inclusions precipitated during the solidification process and the lower the solidification front temperature is during precipitation; （3） when an 82A steel sample was heated to 1087℃, the Ti（CxN1-x） inclusions possess the thermodynamic conditions of decomposition and solid solution; and （4） when 82A samples were heated to 1150 and 1 250℃, the total number of Ti（CxN1-x） inclusions larger than 5μm in diameter decreased by 55.0% and 70.3%, respectively. In addition, although smaller inclusions with diameter less than 2 μm continued to decompose when the sample was heated at 1 250℃ for 2 h and then cooled to 1000℃ in the furnace, the number of inclusions larger than 5 μm in diameter increased.

Synthesis of new two-dimensional titanium carbonitride Ti_(2)C_(0.5)N_(0.5)T_(x)MXene and its performance as an electrode material for sodium-ion battery

Two-dimensional(2D)layered transition metal carbides/nitrides,called MXenes,are attractive alternative electrode materials for electrochemical energy storage.Owing to their metallic electrical conductivity and low ion dif-fusion barrier,MXenes are promising anode materials for sodium-ion batteries(SIBs).Herein,we report on a new 2D carbonitride MXene,viz.,Ti_(2)C_(0.5)N_(0.5)T_(x)(T_(x) stands for surface terminations),and the only second carbonitride after Ti_(3) CNT_(x) so far.A new type of in situ HF(HCl/KF)etching condition was employed to synthesize multilayer Ti_(2)C_(0.5)N_(0.5)T_(x) powders from Ti_(2)AlC_(0.5)N_(0.5).Spontaneous intercalation of tetramethylammonium followed by sonication in water allowed for large-scale delamination of this new titanium carbonitride into 2D sheets.Multilayer Ti_(2)C_(0.5)N_(0.5)T_(x) powders showed higher specific capac-ities and larger electroactive surface area than those of Ti_(2)CT_(x) powders.Multi-layer Ti_(2)C_(0.5)N_(0.5)T_(x) powders show a specific capacity of 182 mAh g^(-1) at 20 mA g^(-1),the highest among all reported MXene electrodes as SIBs with excellent cycling stability.

Effect of Ti-enriched Carbonitride on Microstructure and Mechanical Properties of X80 Pipeline Steel

In this study,two API X80 pipeline steels were fabricated by varying Ti additions,and their microstructures and fracture characteristics were analyzed to investigate the effects of Ti-enriched carbonitride on the tensile properties and Charpy impact properties.Lathy bainite,a mass of matensite/austenite（M/A）,coarse cubic Ti-enriched inclusions,chain-typed Ti-enriched precipitations,weak toughness and high tensile strength were found as consequences of higher amount of Ti content.Those large scale and chain-typed Ti-enriched carbonitrides are one kind of crack sources during fracture.The negative effect of higher amount of Ti on the impact properties is increased with decreased temperature.

THEORETIC CALCULATION OF SPECIFIC ENERGY OF SEMICOHERENT INTERFACE BETWEEN MICROALLOY CARBONITRIDE AND FERRITE

In some research of microalloy steel, such as the precipitation behaviour and the precipitation strengthening of microalloy carbonitride (M(CN)phase)in ferrite, it is essential to know the accurate value of the interfacial energy between M(CN )phase and ferrite. However, this energy cannot be directly measured because the average size of M(CN) particle is only 2-10 nm, thus the deepgoing researches concerned are seriously limited.

THEORETIC CONSIDERATION ON PRECIPITATION STRENGTHENING MECHANISM OF MICROALLOY CARBONITRIDES IN FERRITE

The precipitation strengthening mechanism of microalloy carbonitrides (M(CN) phases) in ferrite is a basic research work on the precipitation strengthening behaviour of microalloy steels. Generally speaking, the precipitation strengthening effect is regarded as the result

Two-Sublattice Thermodynamic Model on Carbonitride Precipitation in Microalloyed Steels Bearing Nb-V-Ti

Based on the two sublattice model of the regular solution,one being metal atom sublattice and another being interstitial atom sublattice,a thermodynamic model for the precipitates of niobium carbonitride,vanadium carbonitride and titanium carbonitride was established to study the starting-temperature of precipitates and the austenite compositions at given temperature in a low carbon steel.The calculation results show that starting-temperature of the precipitation of niobium carbonitride,vanadium carbonitride and titanium carbonitride are 1100℃,920℃ and 1340℃,respectively,the mole fraction of carbonitride precipitates is 8.65×10-4 in the 0.053C-0.0028N-1.28Mn-0.008S-0.031Al-0.046Nb-0.008Ti0.029V-Fe steel.When the N content is from 0.0028% to 0.0056%,the starting-temperature of the precipitation of the titanium carbonitride changes from 1340℃ to 1430℃.And the C content is from 0.053% to 0.07%,the startingtemperature of the precipitation of the titanium carbonitride hardly changes,but the atomic fraction of niobium in the carbonitride obviously increases.

Friction and wear behaviors of TiCN coating based on electrical discharge coating

Titanium carbonitride (TiCN) coating was prepared on 45# carbon steel by electrical discharge coating (EDC), and the compositions, morphology and microstructure of the coating were studied. In addition, its friction and wear behaviors relative to the physical vapor deposition (PVD) TiN coating were investigated. The results show that the TiCN coating features a thickness of 15μm with a primary phase of TiC 0.3 N 0.7 . The wear rates of the two coatings have no clear distinction at low applied loads. However, severe abrasive wear appears in the PVD TiN coating when the applied load exceeds 30 N, while the TiCN coating features better wear resistance. The abrasive wear with coating peelings is found to be the predominant wear mechanism at high applied loads.