Conventional Cast Alloy Research Articles

Microstructural evolution and tensile mechanical properties of thixoformed high performance aluminium alloys

Commercial thixoforming is generally based on conventional aluminum-based casting alloys such as A356 and A357. However, these alloys do not give such high mechanical properties as the alloys that are conventionally wrought such as 2000, 6000 and 7000 series or the high-strength aluminium casting alloys such as 201. In this paper, 201, 2014, 6082, 7075, 7010 and ‘modified’ versions of 2014 (3.87 wt.% Cu, 0.6 wt.% Mg, 0.14 wt.% Si), 6082 (1.29 wt.% Si, 1.21 wt.% Mg) and 7075 (6.01 wt.% Zn, 3.99 wt.% Mg, 2.06 wt.% Cu, 0.12 wt.% Si) were thixoformed. The recrystallisation and partial (RAP) melting route and the cooling slope (CS) casting route were used to obtain the semi-solid feedstock for thixoforming. Microstructural evolution during partial melting was studied at temperatures where the amounts of liquid were comparable for the various alloys. Tensile mechanical properties of thixoformed parts in the T6 condition were determined and compared with those of conventionally wrought alloys and thixoformed high performance aluminium alloys from the literature. The tensile properties of the thixoformed alloy 201 show a significant improvement over permanent mould casting and the tensile properties of the thixoformed 2014, with an optimised heat treatment schedule, were close to those of forged 2014 but with lower elongation to fracture. Good elongation to fracture (19.6%) was obtained for thixoformed ‘modified’ 2014 in the T6 condition, with a yield strength of 270 MPa and a tensile strength of 408 MPa. This yield strength is significantly short of the target wrought 2014 value and the tensile strength is a little short. The elongations to fracture (24.4 and 12.3%) are satisfactory for alloy 6082 and ‘modified’ 6082 but yield strength and tensile strength need to be increased to achieve the wrought 6082 target. The tensile properties for 7075 thixoformed from starting material produced by the recrystallisation and partial melting route are a little better than those of 7075 thixoformed from starting material produced on the cooling slope. Both routes give values close to the wrought target 7075. The yield strength and tensile strength for ‘modified’ 7075 and 7010 are quite close to the wrought target.

A comparison of the sliding wear behavior of a hypereutectic Al–Si alloy prepared by spray-deposition and conventional casting methods

In this study a hypereutectic Al–20Si (wt.%) alloy was synthesized using two different routes: the spray-deposition technique and the conventional casting process. The dry sliding wear behavior of the alloys was investigated under four loads; namely, 8.9, 17.8, 26.7 and 35.6 N. It showed that spray-deposited alloy exhibited an improved wear resistance at the entire applied load range in comparison to the conventional casting alloy. On the basis of observations and analyses on the worn surface and the wear debris, the wear process of the alloys was controlled by different wear mechanism. The dominant wear mechanism for the spray-deposited alloy was oxidative mechanism, and that for the cast alloy was delamination mechanism.

Influences of original alloy microstructure on magnetic properties of isotropic HDDR-treated Nd–Fe–B powder

Influences of original alloy microstructure on magnetic properties of the isotropic hydrogenation-decomposition-desorption-recombination-treated Nd 12.6Fe 79.0Co 2.4B 6.0 powder were studied using two types of starting materials, i.e., the strip cast (SC) alloy and the conventional book-mold cast (BMC) alloy. It was found that the powder prepared from the SC alloy exhibits better I– H loop squareness and higher remanence than the powder from the BMC alloy. The powder obtained from the SC alloy consists of the recombined Nd 2Fe 14B grains with more uniform size, which is thought to be closely related to its good loop squareness. The effect of using the SC alloy could be attributed to the complete elimination of α-Fe phase.

Effect of fcc-hcp phase transformation produced by isothermal aging on the corrosion resistance of a Co-27Cr-5Mo-0.05C alloy

The corrosion resistance of two-phase (fcc-hcp) Co-27Cr-5Mo-0.05C alloys produced by isothermal aging at 800 °C was studied using potentiostatic polarization tests in Ringer’s solution. Critical pitting potentials were estimated from the potentiostatic polarization curves and were found superior to that exhibited by the conventional ASTM-F75 cast alloy used for the manufacture of orthopedic implants. Formation of suitable distributions of hcp embryos (incoherent twin boundaries and stacking faults) prior to and during the early stages of aging required for isothermal fcc-hcp transformation led to a relative reduction of the corrosion resistance of two-phase alloys. However, once the transformation proceeded rapidly, between 4 and 8 hours of aging, the elimination of lattice defects caused a reduction of the dissolution rates and the breakdown potential became nearly independent of the relative amounts of fcc and hcp phases present in the microstructure. This behavior was due to the uniform chemical composition of the two-phase alloys. Concurrent work has shown that the hardness and yield strength of a 50 pct hcp alloy are increased by at least 30 pct without undue ductility losses. Therefore, the results of the present article suggest that these materials are excellent candidates for the manufacture of orthopedic implant devices requiring higher strength than provided by conventional ASTM-F75 materials.

Analysis of corrosion layers on protective coatings and high temperature materials in simulated service environments of modern power plants using SNMS, SIMS, SEM, TEM, RBS and X-ray diffraction studies.

In three different examples, the effects of the oxidation behaviour as well as the microstructural stability of high temperature materials and protective coatings was determined by combining the results of kinetic studies with extensive analytical investigations using, among other techniques, SNMS, SIMS, SEM, TEM, Rutherford back scattering (RBS) as well as X-ray diffraction. 1). The effect of water vapour on the oxidation behaviour of 9% Cr steels in simulated combustion gases has been determined. The effects of O2 and H2O content on the oxidation behaviour of 9% Cr steel in the temperature range 600-800 degrees C showed that in dry oxygen a protective scale was formed with an oxidation rate controlled by diffusion in the protective scale. In the presence of water vapour, after an incubation period, the scales became non-protective as a result of a change in the oxidation limiting process. The destruction of the protective scale by water vapour does not only depend on H2O content but also on the H2O/O2-ratio. 2). The increase of component surface temperature in modern gas turbines leads to an enhanced oxidation attack of the blade coating. Improvements in corrosion resistance and longer lifetime thermal barrier coatings in gas turbines have been achieved by improvement of the high temperature properties of MCrAlY coatings by additions of minor alloying elements such as yttrium, silicon and titanium. 3). The use of oxide dispersion strengthened (ODS) alloys provides excellent creep resistance up to much higher temperatures than can be achieved with conventional wrought or cast alloys in combination with suitable high temperature oxidation/corrosion resistance. Investigation of the growth mechanisms of protective chromia and alumina scales were examined by a two-stage oxidation method with 18O tracer. The distribution of the oxygen isotopes in the oxide scale was determined by SIMS and SNMS. The results show the positive influence of a Y2O3 dispersion on the oxidation resistance of the ODS alloys and its effect on growth mechanisms.

Mold filling of titanium alloys in two different wedge-shaped molds

Pure titanium and titanium alloys are potential materials for the fabrication of cast dental appliances. One important factor in producing sound castings is the capacity of the metal to fill the mold. This study used a wedge-shaped mold to compare the mold filling of titanium with that of conventional dental casting alloys. The metals used were CP Ti, Ti–6Al–7Nb, Ti–6Al–4V, Ti with 1 and 4 wt% Cu and ADA Type III gold alloy and an Ni–Cr alloy. The castings were cut into four pieces parallel to the triangular surface. Mold filling was evaluated as the distance between the tip of the cast wedge and theoretical tip of the triangle. The mold filling of the gold alloy was superior compared to all the metals tested, while the mold filling of the Ni–Cr alloy was the worst. There were no statistical differences at the 30° marginal angle for all the cast titanium metals. At the sharper 15° angle, CP Ti and Ti–6Al–7Nb was superior to both the Ti–Cu alloys. Although the mold filling of titanium was inferior compared to the gold alloy, the data justify the use of titanium for the production of dental appliances.

Microstructure and electrochemical properties of rapidly solidified alloy Ml(NiCoMnTi) 5

The microstructure and electrochemical properties of MlNi 3.7Co 0.75Mn 0.5Ti 0.05 alloys prepared by both rapid solidification and conventional cast methods were comparatively investigated. SEM and XRD studies showed that the microstructure of conventional cast alloy cooled slowly from its melt was of dendrite, where obvious segregation of Mn and trace second phase TiNi 3 were found. However, the rapidly solidified alloy (cooling at a rate of about 10 6 K s −1) was found to be in columnar structure, and contained CaCu 5 type single phase only, Mn segregation was restrained effectively as well. Electrochemical measurements showed that the rapidly solidified alloy had higher discharge capacity, more flat discharge potential plateau and longer cycle life than conventional cast alloy, but its activation process was longer. The improved cyclic stability of rapidly solidified alloy was attributed to its composition homogeneity and the fine columnar structure, which showed a good resistance to pulverization and corrosion during charging/discharging cycles.

磁性材料 Ｎｄ‐Ｆｅ‐Ｂ系等方性ＨＤＤＲ磁石粉末の磁気特性に及ぼす出発合金組織の影響

We investigated influences of original alloy microstructure on magnetic properties of the isotropic HDDR (hydrogenation-decomposition-desorption-recombination)-treated Nd126Fe79.0Co2.4B6.0 powder by comparing two types of starting materials, i.e., the strip cast (SC) alloy and the conventional book-mold cast (BMC) alloy. It was found that utilizing the SC alloy can achieve better I-H loop squareness, and consequently higher remanence in the final powder. The powder prepared from the SC alloy exhibits a more uniform grain structure of the recombined Nd2Fe14B phase, which is thought to be closely related to its good loop squareness. The effect of using the SC alloy is supposed to be attributed to the complete elimination of α-Fe particles before the HDDR treatment.

Corrosion of Au–Pd–In alloy in simulated physiological solutions

The corrosion of Au–Pd–In alloy, which is of great importance in dentistry, has been studied using an electrochemical quartz crystal microbalance (EQCM) in simulated physiological solutions. The alloy was deposited on quartz substrates by means of magnetron sputtering (MS). Analysis performed using X-ray photoelectron spectroscopy showed that the chemical composition of the sputtered deposit was similar to that of the MS target made of conventional casting alloy. Investigations by X-ray diffraction indicated a crystalline structure of the MS alloy. The electrochemical and corrosion behaviour of the Au–Pd–In alloy was studied in three simulated physiological solutions: 0.9 M NaCl, 0.1 M NaCl + 0.1 M lactic acid and artificial saliva. Determination of break down potential was complicated by the anodic gold dissolution due to formation of a chloride complex. The onset of anodic currents, therefore, indicated not the potential at which the passive layer starts to be destroyed, but the exceeding of the Au/AuCl4− equilibrium potential, which does not directly reflect corrosion resistance. The EQCM measurements under open circuit conditions indicated corrosion as an increase in mass, caused by the accumulation of corrosion products on the alloy surface. The increase in mass in acidic solution (pH 2.2) was similar to that in neutral solution (pH 6.5), which implies dissolution of corrosion products to be insignificant.

Effect of casting method on castability of titanium and dental alloys.

Titanium, once considered to be difficult to cast because of its relatively high melting point (1670 +/- 50 degrees C) and strong chemical affinity, can now be acceptably cast using newly developed casting apparatus. The objectives of this study were to examine the castability of commercially pure (CP) titanium using an ultra high-speed centrifugal casting machine and a pressure difference-type casting unit and to compare the castability of titanium with that of conventional dental casting alloys. To determine castability, two types of patterns were used: a mesh pattern of 22 x 24 mm cut polyether thread sieve, and a saucer pattern (24 mm diameter) perforated to create four T-shaped ends. The casting equipment significantly affected the mold filling of both patterns (p < 0.001). The castability indices obtained from both patterns of CP titanium cast in the centrifugal casting machine were significantly (p < 0.05) better than the indices of the castings produced in the pressure-difference casting unit. The radiographs of the saucer pattern cast in the centrifugal casting machine showed some pores that were fewer and smaller in size than the pores found in castings made in the pressure-difference unit. When the ultra high-speed centrifugal casting machine was used with the manufacturer's recommended mold material, the castability of titanium was similar to that of gold alloy or Ni-Cr alloy cast by conventional means.

A comparative study on the electrochemical performance of rapidly solidified and conventionally cast hydride electrode alloy Zr(NiMnM)2.1

The crystalline structure, phase abundance, microstructure and electrochemical properties of hydrogen storage electrode alloy Zr(NiMnM) 2.1 (M=V, Cr) prepared by rapid solidification (melt-spinning) and conventional cast methods have been investigated and compared. Results indicate that conventional cast (CC) alloy is composed of Laves phase, non-Laves phases and a little ZrO 2 , while rapid solidification (RS) alloy are completely composed of Laves phase only. The microscopic structure of RS alloy is completely different from that of the CC alloy. The microstructure of RS alloys is fine grain, while the microscopic structure of CC alloy is coarse dendrite. Obvious differences in electrochemical properties exist in electrodes made of these two differently prepared alloys due to the difference of their phase abundance, composition distribution and microstructure. The discharge capacity of RS alloy is 56 mAh g −1 higher than that CC alloy, it reaches 356 mAh g −1 and its cycle life is much longer than that CC alloy too. But RS alloy are fully only activated after 14 cycles, more difficulty than that CC alloy, which is activated around 9 cycles. As a whole RS (melt-spinning) process improves greatly the comprehensive electrochemical properties of the alloy.

Damping behavior and tribological properties of as-spray-deposited high silicon alloy ZA27

High damping materials allow undesirable mechanical vibration and wave propagation to be passively suppressed. This has proven valuable in the control of noise and in the enhancement of vehicle and instrument stability. The effects of the addition of 5 wt.% of silicon on the damping behavior and friction-wear property of alloy ZA27 were investigated in an effort to develop a new functional material with high damping capacity and good tribological properties. The material was processed by a spray atomization and deposition technique. The damping capacity, as well as the relative dynamic modulus, was measured at frequencies of 1,4 Hz over the 303–573 K temperature range. No peak phenomena were observed for the specimens tested in the temperature range of interest. Wear experiments were carried out on an MM-200 tribometer, the results indicating that the wear resistance and anti-friction properties of the as-spray-deposited high silicon alloy ZA27 were 8.1 and 2.4 times higher than that of conventional casting alloy, respectively, at a load of 300 N. Finally, the operative damping and tribological mechanisms were discussed in the light of the data obtained from its characterization of microstructure, damping capacity and tribological properties.

Microstructural and Magnetic Improvements in Tube-Cast Pr-Fe-B-Cu Alloys Via Heat Treatments and Rapid Upset Forging

ABSTRACTAlloys of Pr-Fe-B-Cu were cast into Cu and stainless steel tubes. It could be seen that a preferred crystallographic orientation was obtained after cooling. Fine platelets of Pr2Fe1 4B matrix phase were formed, surrounded by various grain boundary phases, and there was a significant reduction in the amount of free Fe present, in comparison to conventional slab cast alloys. In order to improve the magnetic properties in the as-cast state, two alternative routes were used. The first involved a series of two step heat treatments to develop an improved microstructure. After an optimum heat treatment of 1000 'C for 24 hours + 500°C for 3 hours, significantly improved magnetic properties were obtained for a 17.5 % Pr alloy; Br = 752 mT, Hci = 613 kAm−1 and BHmax = 96 kJm−3. The second route involved a rapid upset forging [RUF] process, with a strain rate of 11.5 s−1, to hot deform the alloys. Following post-forging heat treatments, properties of Br = 966 mT, Hci = 780 kAm−3 and BHmax = 160 kJm−3 were obtained for a 15% Pr alloy. That nature of the improvements in properties as a result of heat treatments and RUF were investigated and are discussed in the present work.

A current perspective of PM superalloys : W.B.Eisen. (Crucible Research Center, Pittsburgh, USA.) Int. J. Powder Metall., vol 33, no 8, 1997, 62–67

Additive manufacturing (AM) technology is currently undergoing rapid development in the aerospace field. However, due to the intense cracking susceptibility, additive manufacturing of nickel-based single-crystal (SX) superalloys still presents major challenges. In this paper, the crack-free SX superalloy is fabricated directly using pulsed laser. The microstructure and stress rupture property of the additively manufactured SX superalloy after heat treatment are carefully investigated and compared with conventional cast alloy. The results show that the stress rupture life of the AM sample (66.4 h) is longer than that of the cast sample (59.1 h). This is related to the difference of microstructure between AM and cast samples. AM samples have a finer dendritic structure and lower inter-dendritic segregation, which is conducive to solution strengthening and avoids the formation of TCP phase. Besides, the carbides in the AM sample is finer and evenly distributed, which is conducive to precipitation strengthening; The fine carbides are enveloped within layers of γ′ in the AM samples, which avoids the formation of cracks caused by separation of carbides and the matrix. All of those are beneficial to improve stress rupture properties.

Effect of tungsten particle size on properties of infiltrated tungsten-copper compacts: K.S.Hwang. (Taiwan National University, Taiwan.)

Pure titanium and titanium alloys are potential materials for the fabrication of cast dental appliances. One important factor in producing sound castings is the capacity of the metal to fill the mold. This study used a wedge-shaped mold to compare the mold filling of titanium with that of conventional dental casting alloys. The metals used were CP Ti, Ti–6Al–7Nb, Ti–6Al–4V, Ti with 1 and 4 wt% Cu and ADA Type III gold alloy and an Ni–Cr alloy. The castings were cut into four pieces parallel to the triangular surface. Mold filling was evaluated as the distance between the tip of the cast wedge and theoretical tip of the triangle. The mold filling of the gold alloy was superior compared to all the metals tested, while the mold filling of the Ni–Cr alloy was the worst. There were no statistical differences at the 30° marginal angle for all the cast titanium metals. At the sharper 15° angle, CP Ti and Ti–6Al–7Nb was superior to both the Ti–Cu alloys. Although the mold filling of titanium was inferior compared to the gold alloy, the data justify the use of titanium for the production of dental appliances.

Electrochemical noise for evaluating susceptibility of lead–acid battery electrodes to intergranular corrosion

Abstract Operating and cycle life performance of lead–acid batteries is governed in part by intergranular corrosion (IGC) of the positive electrode, which results in significant weight loss by grain dropping. The present paper demonstrates the use of frequency and time domain noise measurements to evaluate the effect of grain boundary structure on the resistance of lead electrodes to IGC. Microstructures processed to contain high frequencies of special crystallographically ordered boundaries were compared with conventional cast alloys. Significant reductions in localisation function and in the time constant for repassivation occur as the proportion of special boundaries in the microstructure increases. This reflects a tendency for these ordered interfaces to repassivate more readily and to promote the formation of a more compact, stable, and dense PbO2-PbSO4 layer. Electrochemical noise measurements demonstrate the potential for minimising localised intergranular attack and extending battery life by incre...

Dentists' opinions on aspects of cast titanium restorations

Objectives: The purpose of this paper was to study dentists' opinions regarding aspects of the clinical use of cast titanium restorations. Methods: Since 1988 more than 10000 cast titanium units of crowns and fixed partial dentures have been produced by the only dental laboratory that produces cast titanium restorations in Norway. A questionnaire on the clinical behaviour of such restorations was mailed to all 72 dental practitioners who were recorded in the computer file of this laboratory. Results and conclusion: In the opinion of the 64 dental practitioners who completed the questionnaire, cast titanium is a useful supplement to conventional casting alloys, particularly because of its favourable cost. It has a satisfactory clinical behaviour, although there may be some problems related to technical and aesthetic aspects.

Comportamiento a tracción a temperaturas ambiente y elevadas de nuevos composites basados en aleaciones hipereutécticas de Al-Si

This work shows the improvement obtained on tensile stress at room and high temperatures of hypereutectic Al-Si alloys. These alloys are produced by a combination of spray-forming, extrusion and thixoforming process, in comparison with conventional casting alloys. Al-25%Si-5%Cu, Al- 25%Si-5%Cu-2%Mg and Al-30%Si-5%Cu alloys have been studied relating their microstructural parameters with tensile stress obtained and comparing them with conventional Al-20%Si, Al-36%Si and Al-50%Si alloys. Al-25%Si-5%Cu alloy was tested before and after semi-solid forming, in order to distinguish the different behaviour of this alloy due to the different microstructure. The properties obtained with these alloys were also related to Al-SiC composites formed by similar processes.

Wear of a spray-deposited hypereutectic aluminium-silicon alloy

This paper compares the wear characteristics of hypereutectic aluminium-silicon alloys processed using two different routes: the more recent spray-deposition technique and the conventional casting process. Unlubricated pin-on-disk wear tests revealed that the spray-deposited alloy has a better resistance to wear than its conventionally-cast counterpart. It is suggested that the increased hardness and the uniform distribution of the fine second phase in the spray-deposited alloy endowed it with a better wear resistance compared to the conventionally-cast alloy over the range of sliding conditions investigated presently.

Fatigue behavior of a single crystal nickel-base superalloy

Many investigations indicate that high cycle fatigue cracks, in general, initiate at pores, inclusions, and grain boundaries in materials. The fatigue strength limit of a single crystal superalloy increases markedly compared to that of a conventional cast alloy, because the number of pores and inclusions in a single crystal superalloy are less than those of both conventionally cast and directionally solidified superalloys. Also, grain boundaries are eliminated in the single crystal superalloy. The fatigue fracture of a single crystal superalloy usually appears to be brittle. Therefore, it is necessary to study the micro-fracture mechanism. This paper presents an investigation of the fracture characteristics and micro-mechanism of fracture in a single crystal superalloy during high cycle fatigue.