Effects of co-addition of titanium and boron on microstructure of superplastic Cr–Mo steels

Abstract

The effects of titanium and boron on the microstructure of a low alloyed Cr–Mo steel with 0·6 wt-%C have been investigated by comparison with a steel containing only titanium and a steel free from both titanium and boron. Each of the steels was subjected to thermomechanical treatment and annealed at 700°C, resulting in small grains of size a few micrometres. The steel containing both titanium and boron possessed the smallest ferrite grains and M₃C carbides of the three examined. This is attributed to a fine dispersion of borides (TiB₂ ) and borocarbides (Ti(C,B)) of size 10 nm in the ferrite matrix through the pinning effect. At the grain boundaries small carbide particles were present which were effective in inhibiting grain boundary migration. The extremely fine borides and/or borocarbides were useful in suppressing intragranular deformation of ferrite grains due to precipitation hardening. This may have assisted in promoting grain boundary sliding, resulting in superior superplastic elongation.     

Effects of intense cooling on microstructure and properties of friction-stir-welded Ti–6Al–4V alloy

Friction stir welding (FSW) was used to join Ti–6Al–4V alloy in air and under intense cooling conditions. The results show that the application of liquid nitrogen is beneficial in decreasing the peak temperature and in reducing the extent of the high-temperature region during welding, leading to a smaller stir zone (SZ). Intense cooling can lead to refined and homogeneous grains in the SZ, resulting in increased microhardness. The FSW joint produced with intense cooling had a tensile strength of 1020?MPa, which is nearly equivalent to that of the base material and is up to 2.6% higher than for the air-cooled joint. The fractographs for both types of joint were characterised by dimples, indicating that the fractures were ductile.     

Influence of Sc and Zr additions on microstructure and properties evolution of Al–Zn–Mg alloy

Journal of Materials Science - In this study, the effects of different Sc?+?Zr compound addition on the tensile properties, impact toughness, stress corrosion cracking (SCC) properties,...     

Effects of post-aging cooling condition on structure and tensile properties of aged Ti–7.5Mo alloy

The present study investigated the effects of post-aging cooling condition on tensile properties of an aged Ti–7.5 wt% Mo alloy. Experimental results indicated that the solution-treated (ST) Ti–7.5Mo samples were comprised substantially of α″ phase, while all aged samples demonstrated the co-existence of α′ and β phases therein. The relative amount of β phase retained in the aged alloy was found sensitive to post-aging cooling condition. Water-quenched (WQ) alloy had the highest β phase content, while furnace-cooled (FC) alloy had the lowest β phase content. The Mo concentration in β phase was also sensitive to post-aging cooling condition. The average Mo concentration in β phase was found highest in FC samples and lowest in WQ samples. Compared to ST samples, all aged samples demonstrated significant increases in yield strength and modulus values, along with decreases in elongation. The effect of post-aging cooling condition on microhardness was similar to that on strength.     

Effects of Cr,Mn, Si,Cu and Zr on microstructure and mechanical properties of high carbon Fe–16Al alloy

Abstract

Effects of alloying elements Cr, Mn, Si, Cu and Zr on the microstructure and mechanical properties of Fe₃Al (Fe–16Al) based alloy containing ～0·5 wt-%C have been investigated. Six alloys were prepared by a combination of air induction melting with flux cover and electroslag refining (ESR). ESR ingots were hot forged and hot rolled at 1373 K and were further characterised with respect to microstructure and mechanical properties. The base alloy and the alloys containing Cr, Mn, Si and Cu exhibit a two phase microstructure of Fe₃AlC_0·5 precipitates in Fe₃Al matrix whereas the alloy containing Zr exhibits a three phase microstructure, the additional phase being Zr rich carbide precipitates. Cr and Mn have high solubility in Fe₃AlC_0·5 precipitates as compared to Fe₃Al matrix whereas Cu and Si have very high solubility in Fe₃Al matrix compared to Fe₃AlC_0·5 precipitate and Zr has very low solubility in both Fe₃Al matrix and Fe₃AlC_0·5 precipitate. No significant improvement in room and high temperature (at 873 K) strengths was observed by addition of these alloying elements. Furthermore, it was observed that addition of these alloying elements has resulted in poor room and high temperature ductility. Addition of Cr, Mn, Si and Cu has resulted in marginal improvement in creep life, whereas Zr improved the creep life significantly from 22·3 to 117 h.     

Sintering behavior and effect of ternary additions on the microstructure and mechanical properties of Ni–Fe-based alloy

The sintering behavior and effect of ternary additions on the microstructure and mechanical properties of Ni–Fe-based alloy were investigated, with the ternary additions Al, Co, Cr, Mo, Ta, and Ti. The effect of the different ternary additions was more obvious when comparing Ni40Fe10X (X?=?Al, Ti) and the rest of the alloys, with the former having better density and hardness than the latter. Sintered densities close to theoretical (≥98%), excluding Ni40Fe10Mo, were achieved. Interestingly, the visible porosity regions in all the samples were very small in agreement of the high sintered densities observed. The shrinkage rate was similar for all the alloys, and three peaks were observed, the first two peaks merged, and overall all the peaks were indicative of the phenomena responsible for good densification. The hardness measurement revealed that samples with poor homogeneity and those with clusters of ternary element addition in the microstructure had no hardness improvement compared to the base binary alloy. For alloys with Al, Cr, and Ti, fracture surface SEM morphology revealed the intergranular fracture of the grains and the ductile tearing of the binding phase, typical dimple structure of a ductile material; therefore, the mechanical properties of these samples are improved, while the rest of the alloys were characterized with peeling of very fine spherical particles and varying grain size and consequently compromising its mechanical properties.     

Structure and mechanical properties of Ti–5Cr based alloy with Mo addition

The effects of molybdenum (Mo) on the structure and mechanical properties of a Ti–5Cr-based alloy were studied with an emphasis on improving its strength/modulus ratio. Commercially pure titanium (c.p. Ti) was used as a control. As-cast Ti–5Cr and a series of Ti–5Cr–xMo (x = 1, 3, 5, 7, 9 and 11 wt.%) alloys were prepared by using a commercial arc-melting vacuum-pressure casting system, and investigated with X-ray diffraction (XRD) for phase analysis. Three-point bending tests were performed to evaluate the mechanical properties of all specimens and their fractured surfaces were observed by using scanning electron microscopy (SEM). The experimental results indicated that Ti–5Cr–7Mo, Ti–5Cr–9Mo and Ti–5Cr–11Mo alloys exhibited ductile properties, and the β-phase Ti–5Cr–9Mo alloy exhibited the lowest bending modulus. However, the Ti–5Cr–3Mo and Ti–5Cr–5Mo alloys had much higher bending moduli due to the formation of the ω phase during quenching. It is noteworthy that the Ti–5Cr–9Mo alloy exhibited the highest bending strength/modulus ratios at 26.0, which is significantly higher than those of c.p. Ti (8.5) and Ti–5Cr (13.3). Furthermore, the elastically recoverable angle of the Ti–5Cr–9Mo alloy (30°) was greater than that of c.p. Ti (2.7°). The reasonably high strength (or high strength/modulus ratio) β-phase Ti–5Cr–9Mo alloy exhibited a low modulus, ductile property, and excellent elastic recovery capability, which qualifies it as a novel implant materials.     

Characterization of microstructure and mechanical properties of laser melting deposited Ti–6.5Al–3.5Mo–1.5Zr–0.3Si titanium alloy

A plate of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si (TC11) titanium alloy is fabricated by laser melting deposition process. Grain morphology and microstructure characteristics and the formation mechanism have been systematically studied. It is shown that the three dimensional macrostructure is a specially alternately arrayed grain morphology of columnar grains and equiaxed grains. This structure is generated by the high temperature gradient in the overlap zone and relatively low temperature gradient in the body zone of the molten pool. Combining the results of the X-ray diffraction (XRD) and the solidification process, it can be inferred that a preferential orientation with the β 〈0 0 1〉 along the deposition direction exists in the as deposited TC11 plate. An ultrafine basket-weave microstructure within the columnar and equiaxed grains is formed due to the rapid solidification process. The lamellar α within the columnar grains is much uniform than that of the equiaxed grains. Room tensile test data have shown that the LMDed material was characteristic of high strength and low ductility compared with the conventional forged materials.     

Effects of heat treatment on microstructure and mechanical properties of twin roll casted Al–5.5Mg–0.02Ti alloy

In the present investigation the Al–5.5Mg–0.02Ti alloy produced by twin roll casting (TRC) process (varying rolling speed, i.e., 3, 4, and 5 rpm) has been subjected to heat treatment for microstructure modification. Grain coarsening at the center of the strip has been observed during heat treatment process. Homogeneous microstructure of the alloys has been achieved by heat treatment process, and it has been found that the time to achieve homogeneous structure depends on the rolling speed. Transmission electron microscope (TEM) studies revealed that undesired Mg rich phase (Mg₅Al₈) has been successfully eliminated by heat treatment process. Fine and equi-axed grains in the alloys obtained by heat treatment process shows high strength and elongation.     

Effect of rare earth–aluminium additions on the microstructure of a semisolid low carbon Fe–B cast alloy

Abstract

The present study investigates the effects of rare earth and aluminium on the microstructures of as cast and heat treated semisolid Fe–B cast alloys. The as cast microstructure of the semisolid modified Fe–B cast alloy consists of the eutectic boride, pearlite and ferrite. Moreover, compared to a net-like distribution of the coarse eutectic borides in the ordinary unmodified alloy, the eutectic boride structures in the semisolid modified alloy are greatly refined and less interconnected. After heat treatment, the phases in the semisolid modified Fe–B cast alloy consist of the boride and martensite. The additions of rare earth and aluminium help to promote the formation of the short rod shaped and round borides in the semisolid Fe–B cast alloy during heat treatment. Compared to the ordinary unmodified alloy, there is no significant change in the boride area fraction but an obvious decrease in average boride area in the semisolid modified alloy.     

Influence of solution treatment on microstructure and mechanical properties of a near β titanium alloy Ti-7333

The effect of solution treatment on the microstructure and mechanical properties of Ti-7333, a newly developed near β titanium alloy, was investigated. Compared to Ti-5553 and Ti-1023, Ti-7333 possesses the slowest α to β dissolution rate, allowing a wider temperature window for processing. The rate of β grain growth decreases with the increase of soaking time and increases with the increase of solution temperature. The β grain growth exponents (n) are 0.30, 0.31, 0.32 and 0.33 for solution treatment temperature of 860 °C, 910 °C, 960 °C and 1010 °C, respectively. The activation energy (Q_g) for β grain growth is 395.6 kJ/mol. Water cooling or air cooling after solution treatment have no significant influence on microstructure, which offers large heat treatment cooling window. However, under furnace cooling, the fraction of α phase increases sharply. α phase maintains strictly the Burgers orientation relation with β phase ({0 0 0 1}_α//{1 1 0}_β and 〈1 1 −2 0〉_α//〈1 1 1〉_β), except the α_p particles formed during forging. The tensile strength decreases with the increase of the solution temperature when only solution treatment is applied, whereas the ductility increases gradually. When aging is applied subsequently, the tensile strength increases with the increase of the solution temperature and the ductility decreases gradually.     

Effect of heat treatment on microstructure and mechanical properties of a new β high strength titanium alloy

Microstructure and mechanical properties of a new β high strength Ti–3.5Al–5Mo–6V–3Cr–2Sn–0.5Fe titanium alloy were investigated in this paper. Both the α/β and β solution treatment and subsequent aging at temperatures ranging from 440 °C to 560 °C for 8 h were introduced to investigate the relationship between microstructures and properties. Microstructure observation of α/β solution treatment plus aging condition shows that the grain size is only few microns due to the pinning effect of primary α phase. The β solution treatment leads to coarser β grain size and the least stable matrix. The size and volume fraction of secondary α are very sensitive to temperature and strongly affected the strength of the alloy. When solution treated at 775 °C plus aged at 440 °C, the smallest size (0.028 μm in width) of secondary α and greatest volume fraction (61%) of α resulted in the highest yield strength (1624 MPa). And the yield strength decreased by an average of 103 MPa with every increase of 40 °C due to the increase of volume fraction and decrease of the size of secondary α. In β solution treatment plus aging condition, tensile results shows that the strength if the alloy dramatically decreased by an average of 143 MPa for every increase of 40 °C because of larger size of secondary α phase than α/β solution treated plus aged condition.     

Influences of boron contents on microstructures and mechanical properties of as-casted near α titanium alloy

Ti-6.5Al-2.5Sn-9Zr-0.5Mo-0.25Si-1Nb-1W-0.1Er-xB(x=0,0.1,0.2,0.4,0.6 and 0.8 wt％)with different boron contents are fabricated for investigation.Influences of boron element and its amounts on phase constitutions,microstructures,textures and compression mechanical properties are carefully studied.With the increasing boron additions,contents of TiB phase increase,and the maximum intensities of tex-tures decrease.Microstructures are significantly and continuously refined after adding boron element and with the increasing boron additions,and turning point of refinement rates for different microstruc-tural parameters is found at 0.2 wt％boron content.Strengths increase monotonously,while elongations increase firstly and decrease afterwards.The maximum value of elongation is acquired at boron con-tent of 0.2 wt％.On the premise of ensuring plasticity,0.2 wt％boron content is the most appropriate amount for microstructural refinement and mechanical properties enhancement for current near α tita-nium alloys.Meanwhile,aspect ratios of TiB whiskers increase with the increasing boron contents.Lots of near equiaxed α grains or α grains with irregular morphologies are discovered around TiB phase.Dis-torted and twisted α grain boundaries are also obviously detected in boron containing alloys.Moreover,premature fracture of alloys containing TiB whiskers is largely influenced by the fracture of these brittle reinforcements.     

Effects of Ca additions on the microstructural stability and mechanical properties of Mg–5%Sn alloy

Mg–Sn based alloys have great potential for high temperature applications because of the formation of the thermally stable Mg₂Sn phase in the as-cast condition. In the present investigation, for further enhancement of the mechanical properties, 0.7, 1.4 and 2 wt.% of Ca was added to the base Mg–5%Sn alloy. The dendritic structure of the base alloy was refined after the addition of Ca. It was found that the Mg–5%Sn–2%Ca alloy had the highest hardness, strength, and creep resistance among all tested materials. This is attributed to the higher volume fraction of CaMgSn second phase particles which act as the main strengthening agent in the investigated system. Results also showed that while long-term annealing treatment softened the base Mg–5Sn alloy, there was not much change in the hardness and strength of the Ca-containing materials, implying that CaMgSn intermetallic particles have successfully increased the microstructural stability of the materials.     

Effects of dynamic mechanical properties on the ballistic performance of a new near-β titanium alloy Ti684

A comprehensive study of the newly developed near-β titanium alloy Ti684 has been carried out to determine the influence of the dynamic strength, dynamic hardness and critical failure strain on the ballistic impact properties. Two heat treatments of Ti684, namely β solution-treatment and α + β solution-treatment followed by aging, were carried out and the results were compared with Ti–6Al–4V. Ballistic impact tests were conducted on 7 mm thick front plates with a 20 mm thick A3 steel backing plate, using 7.62 mm armor piercing projectiles. The ballistic performance was evaluated by measuring the residual depth of penetration (DOP) in the A3 steel backing plates. It was found that the DOP values did not show obvious corresponding relation with both dynamic strength and dynamic hardness. The 800 °C solution +550 °C aged Ti684, which had the maximal dynamic strength, presented the worst ballistic performance, with a maximum DOP of 12.5 mm. In addition, the Ti–6Al–4V plate in the study with highest dynamic hardness did not show the best ballistic performance, having a DOP of 11.86 mm. However, as the critical failure strain increased, the DOP of the A3 steel backings were observed to decrease. This relationship was revealed from post ballistic microstructural observations.     

Effect of duplex aging on microstructure and mechanical behavior of beta titanium alloy Ti–15V–3Cr–3Al–3Sn under unidirectional and cyclic loading conditions

The microstructure and mechanical behavior of beta titanium alloy Ti–15V–3Cr–3Al–3Sn (Ti15-3) under unidirectional and high cycle fatigue (HCF) loading conditions were studied after single aging (SA) and duplex aging (DA). After SA, well-developed grain boundary α and micro precipitate free zones (micro PFZs) were present in the microstructure. Whereas after DA, grain boundary α was poorly developed and micro PFZs were absent. DA resulted in smaller size, higher density and volume fraction of alpha particles. DA led to higher work hardening rate, better strength-ductility combination and higher HCF life. Improved mechanical behavior after DA is explained based on microstructural observations.     

Effects of microadditions of vanadium and boron on age hardening and mechanical properties of Al–Li alloy 8090

Abstract

The effects of micro additions of vanadium and boron on the age hardening, microstructure, mechanical properties, deformation, and fracture behaviour of Al–Li alloy 8090 have been investigated. The addition of 0·6% V to 8090 alloy increases the peak hardness by 13%, the yield strength by 23%, and the ductility by 85% when optimally aged (190°C for 22·5 h). The enhancement of these properties is attributed to the refinement of S′ and δ′ precipitates and the promotion of extensive cross-slip during deformation of the vanadium containing alloys. The same amount of vanadium reduces the impact toughness of 8090 by 50%, which is attributed to the presence of coarse particles of primary Al₁₁V precipitate. Increasing the cooling rate during solidification, or adding 0·1%B, restores and slightly increases the impact toughness of the vanadium containing alloy. The effect of cooling rate is related to the amount and size of Al₁₁V precipitates, which decrease with increasing cooling rate. The addition of boron appears to modify the morphology of the Al₁₁V precipitate.

MST/1584     

Effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy

The effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy were studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), differential scanning calorimeter (DSC), transmission electron microscopy (TEM) and tensile test, respectively. The results show that the mechanical property increases and then decreases with increasing the solution temperature. And the residual phases are dissolved into the matrix gradually, the number fraction of the precipitation and the size of recrystallized grains increase. Compared to the solution temperature, the solution holding time has less effect on the microstructure and the mechanical properties of Al–Cu–Mg–Ag alloy. The overburnt temperature of Al–Cu–Mg–Ag alloy is 525 °C. The yield strength and the elongation get the best when the alloy is solution treated at 515 °C for 1.5 h, is 504 MPa and 12.2% respectively. The fracture mechanism of the samples is ductile fracture.