Micro-alloying of Zn and Ca in vacuum induction casted bioresorbable Mg system:Perspectives on corrosion resistance,cytocompatibility,and inflammatory response

There is an increasing interest in biodegradable materials,such as magnesium,for orthopaedic implants.This is driven by their potential to address challenges like stress shielding and the need for secondary removal surgery.In this study,biodegradable magnesium alloys were produced using the Vacuum Induction Casting technique.The impact of micro-alloying Zn and Ca in Mg-xZn-0.2Ca(x=0.1,0.2,0.3,and 0.4 wt%)alloys on corrosion resistance,cytocompatibility,and early-stage inflammatory response was investigated.XRD and SEM-EDS analysis confirmed the presence of Ca_(2)Mg_(6)Zn_(3)secondary phases in all alloys.The Mg-0.3Zn-0.2Ca alloy exhibited the lowest corrosion rate and an elastic modulus of 36.8 GPa,resembling that of natural bone.Electrochemical measurements indicated a correlation between grain size and secondary phase volume fraction in explaining corrosion behaviour.In vitro degradation in simulated body fluid(SBF)for 21 days showed hydroxyapatite formation on alloy surfaces,aligning with electrochemical studies.In vitro cytotoxicity tests demonstrated the cytocompatibility of all alloys,with Mg-0.3Zn-0.2Ca having the highest cell viability over a 6-day cell culture.Investigation into the inflammatory response with RAW-Blue macrophages revealed the anti-inflammatory properties of Mg-0.3Zn-0.2Ca alloys.Micro-alloying with 0.3 wt%Zn and 0.2 wt%Ca enhanced mechanical properties,corrosion resistance,cytocompatibility,and immunomodulatory properties.This positions the Mg-0.3Zn-0.2Ca alloy as a promising biodegradable implant for bone fixation applications.

Enhanced thermal stability and mechanical properties of high-temperature resistant Al-Cu alloy with Zr and Mn micro-alloying

The high temperature(HT)thermal stability and mechanical properties of Al-5%Cu(AC)and Al-5%Cu-0.2%Mn-0.2 Zr%(ACMZ)alloys from 573 to 673 K were systematically studied.The results displayed that micro-alloying additions of Zr and Mn elements have presented a significant role in stabilizing the main strengthening metastableθ′precipitates at a temperature as high as 573 K.Simultaneously,the HT tensile test demonstrated that ACMZ alloy retained their strength of(88.6±8.8)MPa,which was much higher than that of AC alloy((32.5±0.8)MPa)after the thermal exposure at 573 K for 200 h.Finally,the underlying mechanisms of strength and ductility enhancement mechanism of the ACMZ alloy at HT were discussed in detail.

Influence of Ti(C,N)precipitates on austenite growth of micro-alloyed steel during continuous casting

Austenite grain size is an important influence factor for ductility of steel at high temperatures during continuous casting. Thermodynamic and kinetics calculations were performed to analyze the characteristics of Ti(C,N) precipitates formed during the continuous casting of micro-alloyed steel. Based on Andersen-Grong equation, a coupling model of second phase precipitation and austenite grain growth has been established, and the influence of second precipitates on austenite grain growth under different cooling rates is discussed. Calculations show that the final sizes of austenite grains are 2.155, 1.244, 0.965, 0.847 and 0.686 mm, respectively, under the cooling rate of 1, 3, 5, 7, and 10 ℃·s^(-1), when ignoring the pinning effect of precipitation on austenite growth. Whereas, if taking the pinning effect into consideration, the grain growth remains stable from 1,350 ℃, the calculated final sizes of austenite grains are 1.46, 1.02, 0.80, 0.67 and 0.57 mm, respectively. The sizes of final Ti(C,N) precipitates are 137, 79, 61, 51 and 43 nm, respectively, with the increase of cooling rate from 1 to 10 ℃·s^(-1). Model validation shows that the austenite size under different cooling rates coincided with the calculation results. Finally, the corresponding measures to strengthen cooling intensity at elevated temperature are proposed to improve the ductility and transverse crack of slab.

Micro-alloyed Mg-Ca:Corrosion susceptibility to heating history and a plain problem-solving approach

The exceptionally low corrosion rate(∼0.1 mm y^(–1)in concentrated NaCl solution for 7 days)enables lean Mg-Ca alloys great potential for diverse applications,particularly if relevant properties(e.g.mechanical strength,electrochemical performance,etc.)can be enhanced by thermomechanical processing.However,herein it is demonstrated that the corrosion performance of lean Mg-Ca is susceptible to the heating process.The corrosion rate of Mg-0.15 wt%Ca alloy is remarkably accelerated after annealing even for a short time(4 h at 400℃)because Fe precipitation readily takes place.Fortunately,it is found that micro-alloying with dedicated additional elements is able to solve this problem.Nevertheless,the problem-solving capability is dependent on the element category,particularly the ability of the alloying element to constrain the Fe precipitation.Among the three studied elements(i.e.Sn,Ge and In),only In shows good competence of restricting the formation of Fe-containing precipitates,thereby contributing to retention of the superior corrosion resistance after annealing even at a rigorous condition(24 h at 450℃).The finding creates good foundation for follow-up work of developing lean Mg-Ca-based alloys combining high corrosion resistance,superior electrochemical performance with excellent mechanical properties for applications as biodegradable implants and anode materials for aqueous batteries.

Fe−C micro-alloying effect on properties of Zr_(53)Al_(11.6)Ni_(11.7)Cu_(23.7)bulk metallic glass

(Zr_(53)Al_(11.6)Ni_(11.7)Cu_(23.7))_(1−x)(Fe_(77.1)C_(22.9))_(x)(x=0−2.2,at.%)bulk metallic glasses(BMGs)were prepared by copper mold suction casting method.Their glass forming ability and physical and chemical properties were systematically investigated.The glass forming ability is firstly improved with increasing x,and then decreased when x exceeds 0.44 at.%.Both glass transition temperature and crystallization temperature are increased,while the supercooled liquid region is narrowed,with Fe−C micro-alloying.The hardness,yielding and fracture strength,and plasticity firstly increase and then decrease when x reaches up to 1.32 at.%.The plasticity of the BMG(x=1.32 at.%)is six times that of the Fe-free and C-free BMG.In addition,by the Fe−C micro-alloying,the corrosion potential is slightly decreased,while the corrosion current density increases.The pitting corrosion becomes increasingly serious with the increase of Fe and C content.

Static Recrystallization Behavior of Hot Deformed Austenite for Micro-Alloyed Steel

Static recrystallization behavior of austenite for micro-alloyed steel during hot rolling was studied and the influence (τ-ε diagram) of holding time and deformation at different deformations and isothermal temperatures on microstructuralstate of austenite were discussed. Corresponding to parameter Z in the dynamic recrystallization diagram, parameterY was then introduced to simplify static recrystallization diagrams.

Effect of Chromium Micro-alloying on the Corrosion Behavior of a Low-carbon Steel Rebar in Simulated Concrete Pore Solutions

A new low-cost corrosion-resistant rebar（HRB400 R） was designed and fabricated by chromium micro-alloying. The effects of Cr on the passivation and corrosion behavior of this rebar in the simulated concrete pore solutions were studied systematically, and its improved corrosion resistance was revealed. In the Cl--free saturated Ca（OH）_2 solution, the HRB400 R rebar presented nearly the same passive film and similar passivation ability compared to the common carbon steel rebar. In the long-term immersion corrosion test in the Cl--contained Ca（OH）_2 solution, the HRB400 R rebar presented improved corrosion resistance and obvious longer passivation-maintaining period. Micro-alloying of Cr element in the rebar matrix enhanced its corrosion resistance against Cl--attack and retarded the corrosion initiation in the matrix. In the alkaline Na Cl salt spraying test, the HRB400 R rebar also presented obviously lower mass-loss rate. The enrichment of Cr element in the rust layer improved its retardant effect to the penetration of aggressive medium, and decreased the corrosion propagation rate of the rebar.

Effect of Nb content on strength of Nb micro-alloyed steels

Microstructures and properties of three Nb micro-alloyed steels were studied through hot rolling experiment. The result indicates that the ferrite grain size （dF ） decreases with increasing Nb content （Nb）, and the bainite fraction （fB） increases with increasing Nb content （Nb）. The effect of ferrite grain size （dF） on yield strength （δy） is related to Nb content （Nb）, and the effect of bainite fraction （fB） on yield strength （δy） is unrelated to Nb content （Nb）. Modelling of yield strength （δy） for Nb micro-alloyed steels with high accuracy has been built up with Nb content （Nb） and bainite fraction （fB） taken into account as new parameters, and formulas for ferrite grain size （dF ） and bainite fraction （fB） vs Nb content （Nb） have also been established under the experiment conditions. The research results could provide instructions for industrial productions.

Effect of Mo on the continuous cooling transformation behavior of Nb-Ti micro-alloyed low carbon steel

The effect of molybdenum on the continuous cooling transformation behavior of the micro-alloyed low carbon steel containing niobium and titanium was investigated by a Gleeble 3800 thermo-mechanical simulator. The phase transformation temperature of the steel at various cooling rates was detected. The microstmcture was observed by optical microscope （OM） and scanning electronic microscope （ SEM）, and its Vickers hardness was tested. Based on these, its dynamic continuous cooling transformation （CCT） diagrams were determined. The results show that the transformation temperature from deformed austenite to acicular ferrite （AF） is decreased when Mo is added, and the formation of pro- eutectoid ferrite （F） and pearlite （P） is either inhabited or postponed. Mo can also enlarge the range of the cooling rate in forming AF, and refine the microstructure effectively.

Hot Ductility of Vanadium Micro-alloying Steel Continuous Casting Slabs

The hot ductility of the V-containing micro-alloying steel CC (continuouscasting) slabs and precipitation of vanadium carbide in the tensile specimens were investigated. Theresults indicate that the precipitation ratio and precipitation rate of vanadium in the specimensreach maximum respectively at 900, -825 and 825 deg C. There is still l0 percent-l7 percent ofvanadium precipitated when the deformation temperature decreases to 800-700 deg C. Vanadium largelyaffects the ductility of the steel in the low ductility temperature Region III. Embrittlement ofsteel with higher V content is severer in the region and the embrittlement extends to lowertemperature.

Effect of Ca Micro-Alloying on the Microstructure and Anti-Corrosion Property of Mg0.5Zn0.2Ge Alloy

Magnesium and its alloys have attracting rising attention as one of biodegradable metallic materials.However,the rapid corrosion and severe localized corrosion still hinder their extensive applications in clinics.In this study,micro-alloying of Ca(≤0.1 wt%)into Mg0.5Zn0.2Ge alloy developed in our previous work was explored to further enhance the corrosion resistance and alleviate the localized corrosion of the alloy.The results reveal that the addition of Ca leads to the transformation of the cathodic Mg_(2)Ge phase in Mg0.5Zn0.2Ca alloy into anodic MgCaGe phase in Ca-containing alloys,thereby changing the galvanic couples in alloys during immersion.The preferential dissolution of MgCaGe phase promotes the participation of Ca and Ge into the formation of corrosion products,resulting in the enrichment of Ca and Ge in the outmost of corrosion product layer,which stabilizes and passivates the corrosion product layer on Mg alloy surface.Additionally,the enrichment of Zn at the corrosion interface seems to further hinder the corrosion of Mg matrix.All of these factors confer a slower and more uniform corrosion on Mg0.5Zn0.2GexCa(x<0.1 wt%)alloy,which provides favorable candidates for the further processing to gain suitable biodegradable Mg alloys.

Effect mechanisms of micro-alloying element La on microstructure and mechanical properties of hypoeutectic Al-Si alloys

The rare earth influence on the as-cast micro structures and mechanical properties of aluminum alloys attracted great attentions in the last decades.But up to date no reports can be found on the effect of microalloying element La(La addition is below 0.1 wt.%) on the solidification of hypoeutectic Al-Si alloys.This study carried out solidification experiments with Al-6 Si alloys micro-alloyed by element La.The α-Al grain refinement,the eutectic Si modification and the tensile properties improvement caused by microalloying element La were investigated.The effect mechanisms of La were discussed.It is demonstrated that the addition of La as low as 100 ppm can deprave the more effective heterogeneous nucleation conditions for the eutectic Si caused by the impurity P.The addition of 0.06 wt.% La is sufficient to achieve an ideal α-Al grain refinement,eutectic Si modification and ductility improvement of the alloys.LaAlSi phase forms in the Al-Si alloy with the additive amount of La higher than 0.06 wt.%.It has a tetragonal structure.Micro-alloying element La refines the α-Al grains by working as a surfactant and modifies the eutectic Si by promoting the formation of the significant multiple Si twins.

Effect of Annealing Time on Microstructure and Mechanical Properties of Cold-Rolled Niobium and Titanium Bearing Micro-alloyed Steel Strips

Effects of annealing time on microstructure of cold-roiled niobium-titanium bearing micro-alloyed steel strips were investigated by optical microscopy, scanning electron microscopy, electron back-scatter diffraction （EBSD） and transmission electron microscopy. The complete recrystallization annealing temperature of 670 ℃ and complete annealing time of 9 min were determined using Vickers-hardness testing and EBSD analysis. The ferrite mi-crostructure with spheric cementite particles and nano-scale precipitates of Nb（C,N） in matrix was obtained. The ki-netics of the ferrite grain growth is lowered due to ferrite grain boundaries pinned by the cementite particles, so the ferrite grain size of 5.5 μm remains unchanged among the annealing time ranging from 9 to 30 min. In addition, the strength of tested steel also keeps unchanged with the increase of annealing time. The higher yield strength of ap-proximately 420 MPa can be obtained by grain refinement and precipitation hardening and the higher elongation of approximately 40% and work-hardening exponent of approximately 0.2 can be gained due to grain refinement and presence of cementite particles, indicating that the balance of strength, ductility and forming property is realized.

Effect of coarse TiN inclusions and microstructure on impact toughness fluctuation in Ti micro-alloyed steel

Toughness is an important property for steels used in engineering applications. However, recent toughness testing has shown the existence of a significant fluctuation in toughness in a single rolled plate of titanium micro-alloyed steel. The underlying causes of this fluctuation were investigated by fractography, analysis of microstructure and measurement of inclusions. Coarse and distributed TiN inclusions were responsible for the toughness variation, as they tended to act as the potential cleavage initiators to form micro-cracks. From a calculation of the local fracture stress, the critical size of coarse TiN inclusions for dominating micro-crack propagation was 4.93 μm, and similarly that of ferrite grains was 36.6μm. Under current casting and thermo-mechanically controlled processing schedules, the toughness fluctuation of rolled steel plates can be primarily attributed to the fraction of coarse TiN inclusions larger than 5μm. A corresponding relationship between impact energy and the proportion of coarse TiN inclusions was established. Finally, a normalizing treatment was applied to refine the ferrite grains of rolled steel plates. Despite the presence of coarse TiN inclusions, this refinement in ferrite grains minimized the toughness fluctuation and improved the uniformity of the impact properties of the steel plates.

Effect of micro-alloying La on precipitation behavior, mechanical properties and electrical conductivity of Al-Mg-Si alloys

The rapid industrial development calls for alloys that possess higher comprehensive properties. In this study, the effect of microalloying La addition on the precipitation behavior during artificial aging as well as the mechanical properties and electrical conductivity of Al-Mg-Si alloys were investigated by thermal analysis, microstructural characterizations and properties tests.The results demonstrated that micro-alloying La addition does not change the whole precipitation sequence during the artificial aging of Al-Mg-Si alloys as well as the atomic structure of the precipitates. However, the higher La-vacancy binding energy as well as the strong La-Si and La-Mg interactions can decrease the solubility of Si and Mg in the Al matrix and the β″ precipitation activation energy from 89.9 to 76.7 kJ/mol, leading to the improvement of the strength and electrical conductivity of Al-Mg-Si alloys simultaneously. The microstructural features affecting the strength and electrical conductivity were theoretically discussed in terms of the La addition.

Effects of micro-alloying and production process on precipitation behaviors and mechanical properties of HRB600

Effects of micro-alloying elements and production process on microstructure, mechanical properties and precipitates of 600 MPa grade rebars were studied by using pilot test, metallographic observa- tion, tensile test, thermodynamic calculation and transmission electron microscopy. The results show that the tested steels are composed of ferrite and pearlite, in which the conterlt range of pearlite is 33%-45%. For vanadium micro-alloyed steel, interphase preeipitation Strengthening effect of V can be promoted and the yield strength of tested steels can be increased with increasing V content and de- creasing finishing rolling temperature. The temperature of terminated cooling should be more than 700 ℃ when the water cooling is used. When niobium is added to the steel, more coarse （Nb,V）C,N precipitates are generated at high temperature, so that the solid solubility of precipitated phases of vanadium is reduced and the precipitation strengthening effect of vanadium is weakened.

Strain-induced Precipitation in Ti Micro-alloyed Interstitial-free Steel

Stress relaxation method was carried out on a Ti micro-alloyed interstitial-free （IF） steel at the temperature ranging from 800 to 1000℃. The results show that the softening kinetics curves of deformed austenite can be divided into three stages. At the first stage, the stress has a sharp drop due to the onset of recrystallization. At the second stage, a plateau appears on the relaxation curves indicating the start and finish of strain-induced precipitation. At the third stage, the stress curves begin to descend again because of coarsening of precipitates. Precipitation-time temperature （PTT） diagram exhibited a ＂C＂ shape, and the nose point of the PTT diagram is located at 900 ℃ and the start precipitation time of 10 s. The theoretical calculation shows that the strain-induced precipitates were confirmed as almost pure TiC particles. The TiC precipitates were heterogeneously distributed in either a chain-like or cell-like manner observed by transmission electron microscopy （TEM）, which indicates the precipitates nucleated on dislocations or dislocation substructures. In addition, a thermodynamic analytical model was presented to describe the precipitation in Ti micro-alloyed IF steel, which shows a good agreement between the experimental observation and the predictions of the model.

Effect of Cu on the boron segregation at grain boundaries and vacancy-type defects in ultra-low carbon micro-alloy steels

By thermal neutron irradiation particle tracking autoradiography(PTA)technique,the development of boron segregation at grain boundaries in ultra-low carbon micro-alloy steels was investigated during cooling from 1150°C to 850°C,and the effect of Cu on boron segregation at grain boundaries was discussed.By positron annihilation lifetime(PAL)technique,the changes of vacancy-type defects with temperatures and the effect of Cu on vacancy-type defects in the cooling process were discussed.Results show that,the concentration of boron at grain boundaries increases rapidly at the beginning of the cooling;after that,it begins to decrease;and then,it increases gradually again.The addition of Cu not only increases the concentration of boron at grain boundaries but also speeds up the development process of boron segregation at grain boundaries.During the continuous cooling process,the addition of Cu significantly affects the change of vacancy-type defects with temperatures in ultra-low carbon micro-alloy steels.

Corrosion behavior of low-carbon Cr micro-alloyed steel for grounding grids in simulated acidic soil

To improve the corrosion resistance of steels for grounding grids, a low-carbon Cr micro-alloyed steel was developed （C 1 steel）, and corrosion behavior of Q235 steel and newly developed C1 steel in simulated acidic soil was investigated. The corrosion rate was evaluated with the mass loss measurements, while the corrosion morphology of surface and cross section of rust layer was observed by scanning electron microscopy. The corrosion products were analyzed by energy- dispersive X-ray spectrometry, X-ray diffraction and X-ray photoelectron spectroscopy, and the polarization curve was measured using potentiodynamic polarization method. Results indicated that C 1 steel displayed good corrosion resistance in the simulated acidic soil, of which the corrosion rate was only 30% of that of Q235 steel after corrosion for 360 h. The analysis of rust layer showed that lower carbon content in steel could reduce the tendency of micro cell corrosion and appropriate amount of chromium could improve the corrosion potential of metal matrix. Moreover, the analysis of X-ray photoelectron spectroscopy revealed that the chromium enriched in inner rust layer of C1 steel existed mainly in the form of Fe2CrO4, which facilitated the formation of Cr-goethite and improved the protection of corrosion products.

Enhancement of glass-forming ability and thermal stability of a soft magnetic Co_(75)B_(25)metallic glass by micro-alloying Y and Nb

Soft magnetic Co-based Co-Y-Nb-B bulk metallic glasses(BMGs)without Fe have been developed by micro-alloying Y and Nb into a C075B25 alloy.First,addition of 3^at.%Y promotes the occurrence of glass transition and increases the supercooled liquid stability and magnetic softness.C0_(71.5)Y_(35)B_(25) metallic glass possesses a large supercooled liquid region(△T_(x))of 33 K and low coercivity(H_(c))of l.5 A/m.Subsequent alloying 2-4 at.% Nb into C0_(71.5)Y_(35)B_(25) alloy further enlarges △T_(x) to 50 K,lowers H_(c) to 0.9 A/m,and enables the formation of BMGs with a critical sample diameter up to 2.0 mm.The alloying Nb causes the formation of complex(Co,Nb,Y)_(23)B_(6) competing phase during crystallization and widens the melt undercooling during solidification,which improves the supercooled liquid stability and glass-forming ability,respectively.Co-Y-Nb-B BMGs also exhibit good soft magnetic and mechanical properties,i.e.,lowH_(c)of 0.9-1.2 A/m,relatively high saturation magnetic flux density of 0.36-0.57 T,high yielding strength of 3877-3930 MPa with plastic strain of 0.2%-0.3%,and high Vickers hardness of 1156-1201.The developed soft magnetic Co-based BMGs are promising for applications as structural and functional materials.