TiN Inclusions Research Articles

Thermodynamic and Kinetic Analysis of TiN Precipitation in Nickel-Based Superalloys During Solidification

Large TiN inclusions in nickel-based superalloys promote micropore formation, compromising the mechanical properties of the alloys. However, current research lacks a comprehensive coupled model that considers both solute element microsegregation and TiN precipitation specifically in nickel-based superalloys. This study investigated TiN precipitation during the solidification of IN718 alloys through a combined thermodynamic and kinetic approach. A modified Clyne–Kurz model was applied to account for multi-element microsegregation, enabling an integrated analysis of both microsegregation and precipitation processes. The results indicated that solute elements in the molten alloy segregated to varying degrees during solidification. At an initial nitrogen concentration of 25 ppm, TiN inclusions precipitated when the solid fraction reached 0.256, eventually resulting in a total TiN precipitation of 64 ppm by the end of solidification, while residual nitrogen in the liquid phase decreased to 1.3 ppm. Increasing the initial nitrogen concentration from 10 ppm to 40 ppm advanced the onset of TiN precipitation and raised the total amount from 16 ppm to 126 ppm. Further analysis indicated that cooling rates of 0.03 °C/s, 0.06 °C/s, and 0.18 °C/s did not significantly affect the final TiN accumulation.

Comparative study on the cleanliness and compositional change of alloy steels processed by electroslag remelting and vacuum arc remelting

The cleanliness and compositional change of Ni containing alloy steel processed by electroslag remelting (ESR) and vacuum arc remelting (VAR) were studied. The results show that compared with the electrode steel, the total oxygen content increases in the steel processed by ESR. On the contrary, the total oxygen and total nitrogen content in the steel processed by VAR can be significantly decreased due to the vacuum environment. The number and size of inclusions in steel processed by VAR are significantly decreased, which indicates that the VAR is conducive to improving the cleanliness of steel. Single TiN inclusions are found in both steels processed by ESR and VAR, and oxide inclusions in two steels are (Mg,Al,Ca)O and (Mg,Al)O, respectively. The growth time of TiN inclusions is relatively shorter in the steel processed by VAR, which leads to the thinner TiN layer surrounding the oxide inclusions. During the VAR process, the high temperature and high vacuum conditions promote the volatilization of Mn in steel, leading to decrease of the Mn content in steel. Therefore, extra Mn should be added to the electrode steel before VAR.

Effect of Trace Magnesium Addition on TiN Inclusions and Microstructure in 20CrMnTi Gear Steel

Effect of Trace Magnesium Addition on TiN Inclusions and Microstructure in 20CrMnTi Gear Steel

Investigation of Ti Removal in 45Cr9Si3 Valve Steel by CaF2-Al2O3-CaO-SiO2-MgO-TiO2-Type ESR Slags with Different SiO2 Contents and Their Effects on TiN and Oxide Inclusions

Investigation of Ti Removal in 45Cr9Si3 Valve Steel by CaF2-Al2O3-CaO-SiO2-MgO-TiO2-Type ESR Slags with Different SiO2 Contents and Their Effects on TiN and Oxide Inclusions

Study on the effect of Al-La composite deoxidation on the modification behaviors of TiN and sulfide inclusions in 20CrMnTi gear steel

This article uses experimental and thermodynamic calculations to study the directional modification behavior of TiN and sulfides in 20CrMnTi steel before and after the addition of rare earth La element. The morphologies (SEM) and elemental distributions (EDS) of TiN and sulfide inclusions in steel are characterized using scanning electron microscopy, and the sizes of the inclusions are statistically analyzed. With the addition of rare earth La, the average sizes of TiN and sulfide inclusions in steel decrease, and the proportions of TiN and sulfide inclusions in all inclusions of the steel decrease. The results show that the addition of La element can promote the formation of LaAlO3 in steel, which can be used as the nucleation core of TiN and MnS inclusions in steel, and then form LaAlO3-TiN and LaAlO3-MnS-TiN composite inclusions, which are smaller in size and more uniform in distribution than TiN and sulfide in steel before La element is added. When La is added alone, the average size of TiN inclusion in steel is 2.2 μm. After the deoxidation of Al-La alloy, the average size of TiN inclusion in the steel is 1.9 μm. After Al-La composite deoxidation, the TiN containing inclusions in the steel will be transformed into smaller LaAlO3-TiN composite inclusions. When adding La alone, the average size of sulfide inclusions in the steel is 2.1 μm. When Al-La composite deoxygenation is used, the average size of sulfide inclusions in steel is 1.1 μm, indicating that the Al-La composite deoxygenation has a better improvement effect on sulfide inclusions in steel than the improvement effect of adding La alone.

Investigation of Inclusion Characteristics in Ferrosilicon Killed High Silicon Steels

Industrially, the silicon requirement of liquid steel is often met with ferrosilicon (FeSi) instead of high‐purity silicon addition. FeSi, a silicon‐rich alloy, contains impurities typically inherited from its manufacturing stage. Therefore, FeSi addition results in the formation of complex inclusions in the liquid steel. Herein, a detailed inclusion characterization of the samples obtained from the melting experiments for a wide range of silicon concentrations has been carried out to examine the effect of FeSi impurities. Pure silica inclusions evolve to silica‐ and/or alumina‐based Si–Al–(Ti)–O–(TiN) complex inclusions with the increasing addition of FeSi to the steel melt. Reduction of silica by aluminum or titanium, the presence of titanium in the steel melt, and/or TiN inclusions formed at the periphery of oxide inclusions restrict the growth of oxide inclusions, resulting in small‐sized (average) oxide inclusions. The underlying mechanism of such complex (Si–Al–Ti–O–N)‐based inclusions has been explained with the aid of microstructural characterization and thermodynamic calculations. Moreover, the steel–crucible (alumina) interface has also been investigated for inclusion deposits and crucible–steel interaction.

Pit initiation in quenching and partitioning processed martensitic stainless steels

The present article investigates the influence of chemical composition and phase fractions on the corrosion behaviour of industrially produced quenching and partitioning (Q&P) martensitic stainless steels. Localised corrosion was analysed by scanning Kelvin probe force microscopy (SKPFM) and scanning electrochemical microscopy (SECM) in 3.5 wt.% NaCl solution. SKPFM revealed a Volta-potential difference of around 40 mV between inclusions and the matrix, which is larger than the Volta potential variations within the matrix. This difference in surface potential is a driving force for selective dissolution (corrosion initiation) at inclusions and inclusion/matrix interfaces. SECM detected early pitting initiation, particularly in alloys containing MnS and TiN inclusions. Results suggest that pitting initiation and propagation occur at those specific regions. This study emphasised that irrespective of chemical composition and phase fraction, localised corrosion initiation in Q&P-processed martensitic stainless steels is predominantly governed by the presence of inclusions.

Observation of inclusions and intra-granular ferrite evolutions at the HAZ of low-carbon steel with different thermal histories

This study investigated the formation and growth of intra-granular ferrite with inclusions (TiN, MnS) in the heat-affected zone (HAZ) of a welding joint in low-carbon steels. The relationship between the cooling rate and the density and size of inclusions was analyzed. An orientation relationship akin to the Baker–Nutting relationship was identified between TiN and ferrite, while the orientation relationship between MnS and ferrite approximated the Kurdjumov–Sachs relationship. At low cooling rates, in the absence of nucleation support from TiN and MnS inclusions, the microstructure in the HAZ comprised Widmanstätten ferrite. Additionally, the shape, size, and density of primary ferrites and Widmanstätten ferrite in steels were influenced by sulfur content.

Heterogeneous nucleation interface between NbN(111) and TiN(111) in high-nitrogen austenitic stainless steels: First-principles calculation

Heterogeneous nucleation of NbN induced by TiN inclusions is important to play the role of precipitation strengthening in high-nitrogen austenitic stainless steels. In this work, the atomic structure, interfacial stability, and interfacial fracture toughness of TiN(111)/NbN(111) are investigated based on first-principles calculation. Furthermore, the interfacial bond structure and energy of TiN(111)/NbN(111) are also analyzed with and without Cr doping on the basis of Thermo-Calc phase diagrams. The results indicate that the lattice mismatch between the crystal face of TiN(111) and NbN(111) is lower than 5 %, which reveals that TiN can act as the heterogeneous nucleus for NbN to grow. Besides, the maximum adhesion work at 4.58 J/m2 and the minimum interfacial energy at 1.28 J/m2 are presented on the stacking site of N-Ti TL, which suggests that (Ti, Nb) N phases can precipitate through this interfacial bonding mode. Moreover, from the view of bonding properties on the interface with and without Cr doping, it can be found Cr doping in two layers of the interface can enhance interface stability except for N-Ti TL (2Cr). This work will give promising guidance and theoretical basis for the controllable preparation of high-nitrogen austenitic stainless steels with in-situ precipitated nitride particles.

Lateral Capillary Interaction Between Hexagonal or Triangular‐Shaped TiN Inclusions at the Gas/Steel Interface

Lateral Capillary Interaction Between Hexagonal or Triangular‐Shaped TiN Inclusions at the Gas/Steel Interface

Agglomeration behaviors of different types of complex TiN inclusions in high titanium wear resistant steel

Large-sized titanium-containing inclusion clusters seriously affect the continuous casting and performance of high titanium wear-resistant steel. In the current work, thermodynamic calculations were firstly conducted to predict the formation of various complex TiN inclusions, viz, TiOx-TiN, Al2O3–TiN and LaAlO3–TiN. Based on that, laboratory-scale experiments were designed to prepare samples containing a single type of complex TiN inclusions. The agglomeration characterizes of different complex inclusions were compared by combing in-situ observation based on confocal laser scanning microscopy and Newtonian motion equation. Furthermore, the Kralchevsky-Paunov model was used to study the influences of density and size on the agglomeration behavior of complex TiN inclusions. The result shows that the attractive force between TiOx-TiN complex inclusions increases from 1.93 × 10−18 to 4.34 × 10−17 N, while it was 3.41 × 10−17 to 5.12 × 10−16 N for Al2O3–TiN complex inclusions and 6.42 × 10−18 to 1.14 × 10−16 N for LaAlO3–TiN inclusions. Based on the experimental results and theoretical calculation, the agglomeration tendency of Al2O3–TiN is the strongest due to the considered size and compared to the TiOx-TiN inclusions, the stronger agglomeration tendency of LaAlO3–TiN ones can be attributed to their higher density.

Effect of Al Content on Inclusions in Fe‐15Mn‐xAl‐C Low‐Density Steel

Three experiments of Fe‐15Mn‐xAl‐C (x = 1, 3, 5) low‐density steel with different Al contents are carried out, and the characteristics of inclusions are observed through field‐emission scanning electron microscopy. The results show that the types of inclusions in the three samples are almost the same, mainly Al2O3, AlN, MnS, TiN, Al2O3‐MnS, AlN‐MnS, TiN‐MnS, and Al2O3‐AlN‐MnS. The number percentage of Al2O3 decreases, while the number percentage of AlN increases with the increase of Al content in the three samples. As the Al content increases, the number of inclusions between 1 and 5 μm decreases, while the number between 5 and 10 μm increases. FactSage8.2 software calculation shows that an increase in Al content leads to an increase in the liquidus and a decrease in the solidus of the steel; at the same time, it causes the austenite region to narrow and expands the ferrite region. The change in the solidification route leads to a delay in the solidification fraction of AlN, MnS, and TiN inclusions precipitation. At last, the 2D mismatch theory shows that the mismatch degrees of Al2O3/MnS, AlN/MnS, TiN/MnS, and AlN/Al2O3 are 8.41%, 8.94%, 11.65%, and 11.66%, respectively.

Effects of rare earth Ce on TiN inclusion modifications in 20CrMnTi steel under deoxygenation conditions of Si–Ca–Ba alloy

20CrMnTi steel is widely used in the gear manufacturing field of engineering machinery. The addition of Ti element to steel can effectively improve its low-temperature impact toughness and enhance its mechanical properties. However, during the smelting process of 20CrMnTi, large-sized TiN inclusions are inevitably formed in the steel, which affects its service performance improvement. This paper focuses on the directional modification behaviors of TiN inclusions in 20CrMnTi gear steel by rare earth Ce under deoxygenation conditions of Si–Ca–Ba alloy. The results show that under the deoxygenation conditions of Si–Ca–Ba alone, there are composite inclusions in 20CrMnTi steel with CaAl12O19 as the core and TiN wrapped around the periphery, all of which have sizes greater than 2 μm. This type of inclusion is square or diamond shaped, and the addition of Si–Ca–Ba deoxygenation alone has poor TiN modification effect on gear steel 20CrMnTi. Adding Ce element can effectively improve the nucleation core of inclusions. The CeAlO3–TiN and (CaAl12O19–Ba–Ce)–TiN composite inclusions are formed, and the TiN inclusions are modified in terms of morphology and size. The average size of inclusions decreases from 4.1 to 3.0 μm, which prevented the excessive growth of pure TiN inclusions to some extent.

Effects of refining slag basicity and vacuum treatment on the cleanliness of bearing steel

The effect of vacuum treatment on the cleanliness of low Ti steel treated with low basicity refining slag was studied by analyzing the change of oxygen content and inclusions characteristics in the steel after the interaction between different basicity slags and GCr15 bearing steels and after vacuum treatment. The results show that the oxide inclusions in the steel are mainly MgO·Al2O3 after slag-steel interaction. The low basicity slag refining is beneficial for decreasing the harm of TiN inclusions due to the better low Ti content control. However, the oxygen content and the number of inclusions in the steel increase with the decrease of slag basicity (CaO/SiO2 mass ratio), which means that the decrease in the basicity is disadvantageous to the cleanliness of steel. Typical inclusions in the steel transform into smaller MgO inclusions and MgS–MgO-(MnS) composite inclusions after vacuum treatment, and the oxygen content of steel is decreased to the same level. Furthermore, the size and number density of inclusions are significantly decreased after the vacuum treatment. It indicates that the combined process of low basicity slag refining and vacuum carbon deoxidation can realize the TiN inclusion control and cleanliness improvement of GCr15 bearing steel.

Pit initiation on biomedical alloys-A review.

Biomedical alloys, like many engineering alloys, have chemical or physical heterogeneities at the surface, and such heterogeneities can potentially act as sites for pit initiation. Alloys of particular interest are 316/316L (and 316LVM) stainless steel, nitinol, and CoCr alloys. This review focuses on the sites-generally inclusions-that have been associated with pitting in various studies of biomedical alloys in simulated physiological solutions. The effect of these sites is discussed in relation to factors such as type and size. For both 316/316L stainless steel and nitinol, pitting has been found to initiate at two different types of inclusions: sulfide and oxide inclusions in stainless steel, and carbide and oxide inclusions in nitinol. Sulfide inclusions tend to be the predominant sites for pitting on 316/316L stainless steel, while there is some evidence to suggest that carbide inclusions may be more effective than oxide inclusions for pitting on nitinol. CoCrMo alloys differ from the other two alloys in that, although particles can be present in the form of carbides, the carbides typically do not provide sites for pit initiation except possibly for alloys with a high-C content, certain heat treatments, and when anodically polarized to high potentials. CoNiCrMo differs further in that TiN inclusions can be present in the vicinity of pits and might be associated with them, but irrespective of the initiation site, any pits are unlikely to grow because of repassivation.

Effect of tin inclusion on zinc sulfide thin films properties for photocatalytic applications

Tin doped zinc sulfide (Sn:ZnS) thin films are synthesized by chemical bath deposition (CBD) technique. Tin concentration is varied from 0 to 12 at.-% by a step of 3 at.-%. Structural investigation by X-ray diffraction (XRD) analysis shows the crystallization of the material along the cubic structure as well as an improvement of the crystallinity after Sn inclusion. The surface morphology and film thickness are examined by scanning electron microscopy (SEM) revealing some surface modifications after tin incorporation. Also, some microstructures are observed for the sample elaborated with 9 at.-% Sn. These new microstructures are due to the segregation of tin in the film. Collected optical data show high transmittance in the visible range. The band gap energy is estimated to be about 3.8 eV. Impedance spectra show single semi-circle indicating a single relaxation process. Photocatalytic activity is evaluated and an increment of the degradation efficiency is remarked with the increase of the irradiation time.

Refining mechanism for TiN and solidification structure through a nucleating chain in magnesium-yttrium-treated ultrapure ferritic stainless steel

To investigate the refining phenomena of TiN inclusion and macro-/microstructure through heterogeneous nucleation of δ-Fe at TiN encapsulating oxide during solidification in ultrapure ferritic stainless steel, five samples were prepared, denoted as the initial, low-yttrium-treated, moderate-yttrium-treated, high-yttrium-treated, and magnesium-yttrium-treated samples. Based on the results of TiN inclusions, the minimum value of the average size (2.61 μm) and the maximum value of the number density (346.70 mm−2) were observed after magnesium-yttrium (Mg–Y) treatment. Combined with the mechanism analysis, these results reveal that the TiN can be refined because of the following three reasons: (ⅰ) the pure oxides, possessing low planar and/or linear disregistry with TiN; (ⅱ) the complex oxides, including the phase, which possesses extremely low disregistry with TiN; and/or (ⅲ) the increasing number of the oxides. By comparison, finer macrostructures were yielded with the addition of Y-/Mg–Y-based modifiers because of the decreasing nucleation barrier, and the finest macrostructure with equiaxed grain ratio of 100% and average grain size of 1.099 mm was observed in the Mg–Y-treated sample. Coupled with the results of TiN inclusions, therefore, the refining efficiency of macrostructure increases with the number of TiN. Referring to the results of differential scanning colorimetry, a general rule of solidification for metallic materials has been revealed. In addition, the in-situ nucleation-growth of δ-Fe was observed using high temperature laser confocal microscopy, and the microstructures were refined after Y/Mg–Y treatment. Eventually, the interfacial wetting-lattice mismatch heterogeneous nucleation model is successfully applied to evaluate the refining phenomenon of macro-/microstructures.

TiN Inclusions Formation in Ti-Al Deoxidized Ultra-low Carbon Steel

TiN inclusion in steel is easy to cause surface defects in ultra-low carbon steel. TiN was studied by analyzing their formation mechanisms, compositions, and morphology through SEM (scanning electron microscope) and EDS (energy-dispersive X-ray spectroscopy). Thermodynamic analysis through kinetic simulations of the different stages of RH degassing was conducted by the FactSageTM software package. TiN inclusions can distribute either randomly or in clusters with exogenous inclusions. Most of the TiN inclusions are regular cubic shapes. Some of them have a black center which is alumina inclusion. The alumina inclusions formed by reoxidation can catch TiN inclusions and combine with them because of the strong combining affinity between them. Ti is a strong nitride former in liquid steel, and TiN mostly forms during cooling or solidification. The maximum temperature is approximately 1, 430 °C. The growth of TiN inclusions can be controlled by adjusting the Ti and N contents (N< 30 ppm).

Al-40Sn ALLOY PRODUCED BY SELECTIVE LASER MELTING OF A MIXTURE OF ELEMENTARY POWDERS

Al-40Sn alloy was synthesized by selective laser melting (SLM) of a mixture of elemental powders. In the structure of the alloy, traces of a semi-elliptical melt are observed, the boundaries of the melt regions are decorated with pores and inclusions of tin. The internal structure of melt traces consists of finely crystalline regions with identically oriented columnar Al crystals separated by thin layers of tin. With an increase in laser power, the rate of crystallization of the melt decreases, and the cells of aluminum crystals increase, and with them the thickness of the tin interlayers separating them also increases. The porosity of the alloy decreases slowly with increasing power, and to minimize it, a change in the parameters of the SLM process is required.

Influence of TiN Inclusions and Segregation Bands on the Mechanical Properties and Delayed Crack in Thick NM550 Wear-Resistant Steel.

The formation mechanism of the delayed crack after flame cutting and mechanical properties in thick NM550 wear-resistant steel are studied by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and an electron backscattered diffractometer. The delayed crack is formed at the segregation zone (SZ) located in the center of the 65 mm thick steel plate. The strength of the non-segregation zone (NSZ) with a martensite microstructure is slightly higher than that of SZ with a mixture microstructure of martensite plus bainite, and the plasticity of NSZ is significantly better than that of SZ. There exists a more severe segregation in the SZ, and only a slight segregation in the NSZ. The average grain sizes of the segregation bands in the NSZ and SZ are 15.72 µm and 6.76 µm, respectively. The number density of TiN larger than 5 µm in the NSZ and SZ is 0.031 and 1.156 number/mm2, respectively. Therefore, a high hardness segregation band with fine grains and a high dislocation density, along with the large number of coarse TiN inclusions within it, results in delayed cracking. For TiN inclusions close to the crack, microvoids or microcracks around the TiN are formed, and the delayed crack will propagate along the edge of the TiN or through the TiN inclusions.