Precipitation Of AlN Research Articles

Solidification precipitation behaviour and growth kinetics of AlN inclusions in FeCrAl alloys

AlN inclusions are the major inclusions in FeCrAl alloys and precipitate during solidification. The precipitation behaviour and growth kinetics of AlN inclusions in FeCrAl alloys were theoretically calculated based on the Clyne–Kurz model and a diffusion-controlled growth model. The results indicated that AlN inclusions precipitated at a solid fraction of 0.45. Following precipitation, the Al concentration exhibited a slight decrease compared to scenarios where AlN inclusion precipitation was not considered, although it still showed an increasing trend. Conversely, the N concentration exhibited a significant turnaround, gradually dropping below its initial value. In addition, varying the cooling rate to 0.17, 0.83, 1.67, and 16.67 K/s, the final sizes of AlN inclusions were 46.5, 21.1, 14.8, and 4.7 μm, respectively. Fixing other factors, the solid fractions for AlN precipitation at initial Al concentrations of 4.19, 4.69, and 5.19 wt% were 0.535, 0.45, and 0.365, respectively, and the final sizes of AlN inclusions were 16.2, 14.8, and 13.6 μm, respectively. Similarly fixing the other factors and varying the initial N concentrations to 0.0045, 0.0053, and 0.0060 wt%, the solid fractions of AlN were 0.515, 0.45, and 0.40, respectively, and the final sizes of AlN inclusions were 14.6, 14.8, and 15.0 μm, respectively. This indicates that increasing the cooling rate, increasing the initial Al concentration, and decreasing the initial N concentration could effectively reduce the precipitation size of AlN inclusions. This work provides guidance for the investigation of the precipitation and growth kinetics of AlN inclusions in FeCrAl alloys.

AlN and Nb(C,N) Composite Precipitation Behaviors and Their Effects on Austenite Grain Growth in SCr420H High‐Temperature Carburized Gear Steel

The effects of nitrogen (N) and niobium (Nb) contents on the precipitation behaviors of AlN, Nb(C,N), and AlN‐Nb(C,N) precipitates and austenite grain growth during the pseudo‐carburizing process are investigated for the carburized steel SCr420H. The results indicate that an increase of N content from 0.011% to 0.019% leads to the emergence of fine and uniform austenite grain structure in the sample while being held at 930 °C for 6 h, which is attributed to a notable rise in the number density of AlN and a decrease in the coarsening rate of AlN. In the steel containing 0.023% Nb, the composite precipitates AlN‐Nb(C,N) play a primary role in the pinning effect on austenite grains growth. The isolated Nb(C,N) and AlN precipitates have minor pinning effects due to their very low volume fractions. Nb(C,N) cap forming on AlN substrate obeys the Shoji–Nishiyama orientation relationship. The favorable lattice matching between AlN and Nb(C,N) and accelerated coarsening rate of Nb(C,N) cap decrease hindrances to the nucleation, growth, and coarsening of Nb(C,N) on AlN substrate. Meanwhile, these simultaneous effects also suppress the same processes for the isolated Nb(C,N) in the matrix.

The Effect of Rare Earth Y on the Inhibitor Precipitation Behavior of Strip‐Cast Grain‐Oriented Silicon Steel

0.3 mm‐thick grain‐oriented silicon steel sheets with varying Y contents are produced via twin‐roll strip‐casting and two‐stage cold rolling process. This study primarily investigates the evolution of microstructure, texture, and precipitation along the processing. Specifically, the effect of rare earth Y on second‐phase particle precipitation in ultralow carbon grain‐oriented silicon steel is examined. Results indicate that higher Y content will consume beneficial inhibitor elements such as S and N, leading to the formation of coarse rare earth inclusions (≈10 μm) in the cast strip. This significantly diminishes inhibition ability and magnetic induction (B8 = 1.58 T≈1.71 T). On the contrary, the addition of trace Y can accelerate the precipitation of inhibitors. During the intermediate annealing stage, steel with trace Y exhibits a significant enhancement in precipitate distribution density (from 2.8 μm−2 to 13.6 μm−2), and the final magnetic induction B8 increases from 1.86 T to 1.91 T compared to steel without Y. In addition, the results of first‐principle calculations based on density functional theory reveal that the doped Y atom prefers to segregate at the Al–N interface, and the interface energy reduces from 1.871 J m−2 to 1.024 J m−2, thereby promoting the precipitation of AlN.

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.

Effect of rare-earth Ce on the texture of non-oriented silicon steels

Abstract Macroscopic and microscopic textures of non-oriented silicon steel hot rolled sheets with different rare-earth Ce contents were investigated using X-Ray Diffraction, Electron Back Scatter Diffraction, and field emission scanning electron microscopy, and the magnetic properties of the cold-rolled annealed sheets were examined using a silicon steel sheet testing system. The results show that the addition of rare-earth Ce reduces the proportion of unfavorable γ texture intensity and texture {111} and enhances the proportion of favorable η texture intensity and texture {100} and {110} in the steel. Magnetic property tests show that rare-earth Ce favors the reduction in test steel loss and the increase in magnetic susceptibility. The main reason is that rare-earth Ce combines with O and S in steel to form large-size inclusions, which preferentially precipitate in the liquid steel and inhibit the precipitation of fine AlN and MnS inclusions, while denaturing the inclusions to spherical composite inclusions such as Ce2O2S-MnS, CeS-AlN, and CeAlO3, thus exerting a good effect of purifying the liquid steel and denaturing the inclusions.

Modeling the Precipitation of Aluminum Nitride Inclusions during Solidification of High‐Aluminum Steels

High‐aluminum advanced high‐strength steels have received increasing interest due to their excellent combination of strength and ductility. The control of nonmetallic inclusions in steel is among the most important issue for the production of high‐aluminum steel. This study proposes a model for the evolution of size distributions of AlN inclusions during solidification of steel based on the Kampmann–Wagner numerical model and microsegregation calculation. Both homogeneous (pure AlN) and heterogeneous precipitations (AlN+oxide or MnS) are described using homogeneous nucleation and free growth models of Greer et al. respectively. The model is applied to calculate the size distributions of AlN in high‐Al (up to 5%) Fe–Cr–Al steels and high‐ and medium‐manganese steels and validated by the experimental data in the literature. The model correctly describes the influence of cooling rates on the precipitation of AlN in Fe–Cr–Al steels and high‐manganese steels, and the sizes of AlN are reduced and the number densities of AlN inclusions are increased by increasing the cooling rate. The effects of nitrogen and aluminum concentration in medium‐manganese steel on inclusion precipitation are investigated by the model calculation. The increases in nitrogen and aluminum concentration facilitate the homogeneous precipitation of AlN inclusions.

Characteristics of AlN Precipitation and Growth During Solidification of FeCrAl Stainless Steel

Characteristics of AlN Precipitation and Growth During Solidification of FeCrAl Stainless Steel

Re-Austenitisation of Thin Ferrite Films in C–Mn Steels during Thermal Rebound at Continuously Cast Slab Corner Surfaces

The influence of primary cooling and rebound temperature at C–Mn slab corner surfaces during continuous casting on ferrite film transformation and AlN precipitation was investigated. Laboratory simulations included primary cooling to minimum temperature, Tmin, rebounding to various maximum temperatures, Tmax, followed by secondary cooling. The negative effect of a low Tmin on hot ductility could not be readily reversed, even at relatively high temperatures. Quantitative metallography was employed to study the evolution of the microstructure during rebounding and secondary cooling. Following primary cooling to temperatures just above the Ar3, thin films of allotriomorphic ferrite formed on the austenite grain boundaries. These films did not completely transform to austenite during the rebound at 3 °C/s up to temperatures as high as 1130 °C and persisted during slow secondary cooling up to the simulated straightening operation. Whilst dilatometry did not indicate the presence of ferrite after high rebound temperatures, metallography provided clear evidence of its existence, albeit in very small quantities. Coincident with the ferrite at these high temperatures was the predicted (TC-PRISMA) grain boundary precipitation of AlN in bcc iron during the rebound from a Tmin of 730 °C. Importantly no thin ferrite films were observed, and AlN precipitation was not predicted to occur when Tmin was restricted to 830 °C. Cooling below this temperature promotes austenite grain boundary ferrite films and AlN precipitation, which both increase the risk of corner cracking in C–Mn steels.

Effect of Cooling Rate and High N Content on the Precipitation and Growth of AlN Inclusions in Fe–23Mn–2Al–0.08 V High‐Manganese Nonmagnetic Steel

Industrial experiments are carried out to investigate the precipitation and growth of AlN in Fe–23Mn–2Al–0.08 V steel with nitrogen content up to 80–92 ppm. AlN inclusions can be precipitated before solidification. The morphologies of AlN are mainly divided into hexagonal and needle‐like shapes. With the cooling rate decreasing from 36.66 to 0.71 K s−1, the equivalent diameters of typical AlN increase from 7.56 to 24.20 μm, and the total amount decreases from 203.01 to 60.00 mm−2. The relationship between the cooling rate and the number density is obtained: . The element segregation analyzed by electronic probe microanalyzer shows that aluminum concentration is low in interdendritic regions but high in dendrites. Aluminum segregation is very weak, and there is almost no nitrogen segregation. Thermodynamic calculation shows that AlN can precipitate before solidification with the nitrogen content higher than 58 ppm. The predicted results of AlN growth by kinetic analysis method can well reveal the growth trend. The nitrogen content (≥58 ppm) has a negligible effect on the size of AlN when the cooling rates are 3.02 and 0.71 K s−1, while the cooling rate has a significant effect on the size of AlN.

Effects of the Cooling Rate and Recovery Temperature on the Growth of AlN Precipitates in Gear Steel

During the continuous casting and rolling process of gear steel, AlN precipitation often causes surface cracks on the cast slab. Rapid cooling of the slab surface is a new concept to inhibit AlN and improve the cracking resistance, but it requires further investigation for practical application. Here, the effects of the cooling rate and recovery temperature on AlN growth behavior in gear steel are investigated by designing five cooling conditions. A mathematical model to describe the growth characteristics is constructed based on Ostwald ripening theory. The experimental results show that the cooling rate significantly influences the size and quantity of AlN. When the cooling rate increases from 3.0 to 5.0 °C s−1, the average diameter of AlN decreases from 133.6 to 75.8 nm and the number density of AlN decreases from 6.8 × 105 to 2.1 × 105 cm−2. The calculated results show that AlN has maximum size, which significantly decreases with decreasing temperature. When AlN reaches the maximum size, it stops growing. AlN growth during the cooling process mainly occurs above 800 °C. Therefore, a high cooling rate and a recovery temperature lower than 800 °C are key to inhibiting AlN precipitation and improving the cracking resistance.

AlN precipitation during steel solidification using CA model

AlN precipitation during steel solidification using CA model

Precipitation Behavior of AlN Inclusions in Fe-0.5Al-2.0Mn Alloy Under Continuous Unidirectional Solidification Process

Medium Manganese Transformation Induced Plastic (Mn-TRIP) steels are expected to be a new generation of advanced high strength sheet steels due to their excellent balance between material cost and mechanical properties. During the solidification process, AlN precipitates at the grain boundary, which leads to the serious deterioration of hot ductility. However, the precipitation of AlN in Mn-TRIP steel has not been clear. In this study, the chemical compositions, morphology, size distribution, and the precipitation behavior of AlN inclusion in an Fe-0.5Al-2.0Mn alloy were studied under the continuous unidirectional solidification process. The results show that there are two types of nitride inclusions in the Fe-0.5Al-2.0Mn alloy: AlN inclusion and complex inclusion of Al2O3-AlN. The planar sections of most AlN particles are hexagonal. Based on the thermodynamic calculation, it was found that the content of Al has a large effect on the stability of Al2O3 and AlN. When the content of Al increases, the molten iron can be changed from saturated by Al2O3 to saturated by AlN. During the solidification process, the precipitation of Al2O3 inclusions occurred at the beginning of the solidification process. The precipitation of AlN inclusions occurred when the contents of Al and N exceeded the equilibrium value and grew until the end of the solidification. The precipitation conditions of AlN inclusion in the Fe-0.5Al-2.0Mn alloy during the solidification process were discussed. The precipitation and the amount of precipitate of AlN inclusions depend on the initial contents of Al, N, and O. It was found that the precipitation of AlN inclusions can be controlled by reducing the initial content of N to less than 0.0072 mass%.

Solute cluster-induced precipitation and resultant surface hardening during nitriding of Fe–Al–V alloys

The small amount (0.1 at%) of V addition to Fe–Al alloys promotes AlN precipitation during nitriding and results in substantial surface hardening, in contrast to the normal sluggish precipitation kinetics of AlN during nitriding of Fe–Al binary alloys. The addition of V to Fe–Al alloys can increase the surface hardness to a greater extent than the addition of Ti. First-principles calculations of the interaction energy between an Al atom and an N–s cluster (s = V, Ti, Cr, or Al) show that a V–N cluster has an attractive interaction with an Al atom, and this interaction is stronger than that between a Ti–N cluster and an Al atom, in good agreement with the greater hardening induced by V addition than by Ti addition. These experiments and calculations indicate that solute clusters not only contribute directly to the hardening but also induce alloy nitride precipitation.

Toward energy-efficient physical vapor deposition: Routes for replacing substrate heating during magnetron sputter deposition by employing metal ion irradiation

In view of the increasing demand for achieving sustainable development, the quest for lowering energy consumption during thin film growth by magnetron sputtering becomes of particular importance. In addition, there is a demand for low-temperature growth of dense, hard coatings for protecting temperature-sensitive substrates. Here, we explore a method, in which thermally-driven adatom mobility, necessary to obtain high-quality fully-dense films, is replaced with that supplied by effective low-energy recoil creation resulting from high-mass metal ion irradiation of the growing film surface. This approach allows the growth of dense and hard films with no external heating at substrate temperatures Ts not exceeding 130 °C in a hybrid high-power impulse and dc magnetron co-sputtering (HiPIMS/DCMS) setup involving a high mass (m > 180 amu) HiPIMS target and metal-ion-synchronized bias pulses. We specifically investigate the effect of the metal ion mass on the extent of densification, phase content, nanostructure, and mechanical properties of metastable cubic Ti0.50Al0.50N based thin films, which present outstanding challenges for phase stability control. Ti0.50Al0.50N based thin films are irradiated by group VIB transition metal (TM) target ions generated by Me-HiPIMS discharge, in which Me = Cr (mCr = 52.0 amu), Mo (mMo = 96.0 amu), and W (mW = 183.8 amu). Three series of (Ti1-yAly)1-xMexN films are grown with x = Me/(Me+Al+Ti) varied intentionally by adjusting the DCMS powers, while y = Al/(Al+Ti) also varies as a result of Me+ ion irradiation. Results reveal a strong dependence of film properties on the mass of the HiPIMS-generated metal ions. All layers deposited with Cr+ irradiation exhibit porous nanostructure, high oxygen content, and poor mechanical properties. In contrast, (Ti1-yAly)1-xWxN films are fully-dense even with the lowest W concentration, x = 0.09, show no evidence of hexagonal AlN precipitation, and exhibit state-of the-art mechanical properties typical of Ti0.50Al0.50N grown at 500 °C. The process energy consumption is lowered by 64% with no negative impact on the coating quality. TRIM simulations provide an insight into the densification mechanisms.

Interaction of Si and Al and Its Effect on AlN Precipitation in Ferritic Fe at 1373 K to 1473 K

To investigate the effect of Si on Al and AlN precipitation in ferritic Fe, high-temperature thermochemical equilibrium experiments were conducted on Fe-Si-Al foils and Ag-Si-Al alloys at 1373 K, 1423 K, and 1473 K. Using the activity coefficient in the infinite dilute solution and the self-interaction parameter of Si in ferritic Fe, the interaction parameter between Si and Al in solidified ferritic Fe was found to be a positive value, which corresponds to a repulsive relationship. And its temperature dependence could be also determined as follows. $$ e_{\text{Al}}^{\text{Si}} = \frac{3025}{T} - 1.73 $$ Considering the effect of Si on the activity coefficient of Al, the solubility of AlN in ferrite Fe was investigated and compared with the conventional estimation. It could be confirmed that the stable region of AlN formation becomes larger due to the repulsive relationship between Si and Al in the present research.

Effect of Heat Treatment Process on Microstructure and Crystallography of 20CrMnTiH Spur Bevel Gear

Obtaining excellent mechanical properties of spur bevel gear has been widely emphasized, owing to its indispensable effect on momentum. However, the conventional long-time and high-temperature heat treatment can cause microstructure coarsening, which dramatically decreases the mechanical properties. Since the normalizing process can significantly modulate the mechanical properties of spur bevel gears by adjusting their microstructure and crystallography behaviors, in the present study, the normalizing before or after carburizing heat treatment processes (NBCP and NACP, respectively) were proposed. The effect of heat treatment processes on the microstructure and crystallography of gear specimens was investigated. The results show that both NBAP and NACP had a strong effect on microstructure refinement and hardness improvement compared to the conventional process. NBCP raised the tendency for AlN precipitation, which could retard the microstructure coarsening during carburizing. Furthermore, NACP directly promoted the precipitation of globular Cr-rich M3C carbides which achieved the strongest pinning effect and brought about extremely fine microstructure. For crystallographic analysis, the 24 martensite variants in all gear specimens held Kurdjumov–Sachs orientation relationship to parent austenite. The orientations of martensite variants in gear specimens applying conventional process and NBCP were distributed regularly. However, the orientations of martensite variants in NACP gear specimen did not follow the strict rule for variant selection inside prior austenite grains owing to the distortive effect of diffuse M3C carbides on the matrix, and the adjacent martensite variants possessed less sharing of {110} habit plane compared to NBCP and conventional process.

Influence of Ru-addition on thermal decomposition and oxidation resistance of TiAlN coatings

Doping element into transition metal nitride coatings to optimize their performance against machining has attracted wide research interests. Here, we report the influence of Ru-addition concerning the thermal decomposition and oxidation behavior of TiAlN coatings. Incorporation of Ru results in a structural transformation of cubic Ti0.46Al0.54N and Ti0.43Al0.50Ru0.07N into mixed cubic and wurtzite Ti0.34Al0.51Ru0.15N. With 5 at.% Ru-addition, a comprehensive improvement both in hardness (from ~29.94 to 33.15 GPa) and in fracture resistance (raising the H3/E2 ratio by ~39.8%) is obtained. However, further addition of Ru leads to a drop in hardness (to ~26.09 GPa) for Ti0.34Al0.51Ru0.15N due to the precipitation of wurtzite-structure AlN. Moreover, Ru-containing coatings exhibit a later occurrence of spinodal decomposition, indicating their better thermal stability in comparison with Ti0.46Al0.54N. Nevertheless, the Ru-addition accelerates the transformation from anatase to rutile and hence causes the degeneration in oxidation resistance. Additionally, a mixed oxide scale including Al2O3, RuO2, and TiO2 is formed on the surface of Ti0.34Al0.51Ru0.15N coating at the early stages of oxidation. Both this porous oxide scale and high density of grain boundaries allow the rapid inward diffusion of oxygen, which is also responsible for the inferior oxidation resistance of our Ru-containing coatings. Based on the comprehensive improvement in hardness and thermal stability, the tool life can be improved by ~32% through 5 at.% Ru addition under certain machining condition.

Cubic-structure Al-rich TiAlSiN thin films grown by hybrid high-power impulse magnetron co-sputtering with synchronized Al+ irradiation

Adding Si into transition-metal nitride hard coatings is known to enhance mechanical properties and oxidation resistance. At the same time, however, Si promotes precipitation of wurtzite-structure AlN in Ti1-xAlxN during deposition by magnetron sputtering or cathodic-arc-evaporation, resulting in a decrease in layer hardness. Here, we report nanocomposite films of metastable cubic NaCl-structure TiAlSiN deposited using a hybrid approach combining high-power impulse magnetron sputtering (HiPIMS) from an Al target with DC magnetron sputtering (DCMS) from TiSi targets (Al-HiPIMS/TiSi-DCMS) in which a substrate bias is synchronized to the metal-rich portion of each HiPIMS pulse. The Al/(Al + Ti) ratio is varied from 0.26 to 0.77 by adjusting the TiSi target power, while the Si content ranges from 7.6 to 10.3 at.%. Cubic-structure TiAlSiN solid solutions are obtained with a maximum Al/(Al + Ti) atomic ratio of 0.59 and 9.4 at.% Si. Excess Si segregates to grain boundaries to form a SiNx-rich tissue phase. The hardness H and elastic modulus E of cubic TiAlSiN films increase from H = 19.4 ± 1.7 and E = 322 ± 12 for TiAlSiN layer with Al/(Al + Ti) = 0.26 to H = 37.3 ± 1.3 and E = 388 ± 12 GPa for TiAlSiN layer with Al/(Al + Ti) = 0.59. The TiAlSiN films also exhibit a low intrinsic stress (−0.55 to 0.62 GPa), resulting in a combination of properties: superior hardness and low stress.

Effect of heating rate of final annealing stage on secondary recrystallization in grain-oriented silicon steel

A grain-oriented silicon steel sheet was manufactured by slab reheated at “medium temperature” and two-stage cold rolling method. The function of heating rate on secondary recrystallization in grain-oriented silicon steel was investigated. The results show that: compared with 30 °C/h heating rate, the initial temperature of the secondary recrystallization can increase by 10 °C at the heating rate of 20 °C/h. Furthermore, the temperature region of secondary recrystallization also extended either with the increased heating rate. Even though the inhibitors maintain AlN, complex precipitation of AlN and sulphide in both heating rate, the average diameter and Zener factor of inhibitors are distinct. Inhibitors in the route of 20 °C/h heating rate express stronger inhibition than that of 30 °C/h, and the average diameter and Zener factor are 17.519 nm and 3.925 × 10−4 nm−1, respectively. In addition, more Goss texture component and less γ-fiber texture ({111}//ND) component form at the heating rate of 30 °C/h than 20 °C/h at 1000 °C, but the final Goss texture component of 20 °C/h is greater than 30 °C/h. The average grain size of the final annealing sheets increased with the heating rate decreasing from 30 °C/h to 20 °C/h, and iron loss reduced by 0.05 W/Kg, the magnetic induction intensity increased by 0.025 T.

Effect of Cooling Rate on AlN Precipitation in FeCrAl Stainless Steel During Solidification

The effect of cooling rate on the evolution of AlN inclusions precipitated during solidification in FeCrAl stainless steel was investigated using an experimental study and thermodynamic and kinetic calculations. The number and size of AlN inclusions precipitated under different cooling rates were examined with the feature function of the field-emission scanning electron microscope. A model combining micro-segregation and the diffusion-controlled growth model was set up to determine the mechanism of AlN particle growth. The results showed that AlN precipitates in the mushy zone. The size of AlN particles decreases and the number of AlN particles increases with increasing cooling rate, whereas the volume fraction is essentially unchanged. The AlN particles grow during solidification after the content of solutes in molten steel has exceeded the concentration in equilibrium with AlN. The nitrogen content varies significantly with the cooling rate during solidification. Increasing the cooling rate and reducing the nitrogen content in the molten steel can reduce the AlN particle size in FeCrAl alloys as the growth time decreases.