DIMENSIONAL CHANGES OF SINTERED Fe-Ni,Fe-Cu,Fe-Ni-Cu ALLOYS

Abstract

Sintered alloys of the Fe-Ni, Fe-Cu, and Fe-Ni-Cu systems have been investigated by using single-pressing, double-pressing and hot-forging techniques. Different iron powders containing 0-6 wt.-% nickel or 0-5 wt.-% copper, also (for the ternary system) 0-5 wt.-% of both nickel and copper, were compacted and sintered and the effect of the additions on dimensional changes was studied. The influence of particlesize, compacting pressure, sintering temperatures, and furnace type on dimensions has been determined.     

STUDIES ON THE ACTIVATION-SINTERING OF IRON POWDER

Abstract

A study of the sintering behaviour of iron compacts containing additions of tin up to 1 wt.-% has been made. A tensile strength of 234 MN/m² (34 x 10³ lbf/in²) has been achieved with an optimum tin addition of 0·5 wt.-%, sintering being carried out for 10 min at 1100°C (1373 K) in a reactive halide atmosphere. Combination of the two ‘activating’ techniques (addition of tin and sintering in a reactive atmosphere) permits current properties to be attained at considerably lower sintering temperatures or sintered densities, and is much more effective than when they are applied individually. A tensile strength of 165·3 MN/m² (24 x 10³lbf/in²), achieved by sintering at 1200°C (1473 K) for 10 min with an addition of 0·5 wt.-% tin can be obtained by reactive-sintering the same composition at 900°C (1173 K) for 10 min. Alternatively, the density of the part can be reduced from 6·7 to 6·2 g/cm³ with no loss of strength or elongation. Tin in excess of 0·5 wt.-% causes deterioration in properties under the sintering conditions studied and a reason for this is cited. The improvements in properties are lost also if admixed lubricant is used in the compactionprocess.     

Effect of carbon content,sintering temperature,density, and cooling rate upon properties of prealloyed Fe–1·5Mo powder

Abstract

Mixtures of prealloyed Fe–1·5Mo (Astaloy Mo) with and without additions of 0·5–1·2 wt-%C were prepared and their sintering, as well as their mechanical, properties investigated under different process conditions. It was found that carbon content, sintering temperature, and cooling rate had marked effect on physical and mechanical properties. Sintered density decreased with increase in carbon content and sintering temperature. On the other hand, UTS, TRS, and hardness values improved with up to 0·8 wt-%C addition, sintering temperature, and cooling rate. Percentage elongation decreased with increase in carbon content and cooling rate, but was higher for specimens sintered at higher temperatures. The as sintered microstructures consisted of either fine or coarse pearlite, upper or lower bainite, and their mixture depending on the carbon content and cooling rate. The heat treated mechanical properties showed some improvement for the specimens containing 0·5 and 0·8 wt-%C. It became evident that a variety of ternary low alloy steels consisting of Fe + 1·5Mo + 0·5–0·8 wt-%C can be produced and used in the as sintered or heat treated conditions for PM structural parts having good physical and mechanical properties as well as high dimensional accuracy with acceptable microstructures.     

Synthesis and Characterization of Novel Chromium-Free Nickel Alloy Electrode Materials

The synthesis of two Cr-free nickel-based alloys designated as 1S with 6.5 pct Mn and 2H without Mn of compositions varying between 40 to 43.5Ni, 20Mo, 22 to 25Fe, 10Cu, 6.5 to 0Mn, 1Ti, and 0.5Al (wt pct) as filler materials for TIG welding application was performed. New filler materials were developed to reduce carcinogenic hexavalent chromium (Cr⁶⁺) fumes generated during the welding of 300 series austenitic stainless steel. The Cr-free nickel alloys were characterized for microstructure and mechanical properties. The developed alloys showed good microstructure stability in as-cast and solution-treated conditions. A material properties simulation software JMatPro predicted that 2H alloy has 2 wt pct more γ (solid solution) phase than in 1S but has 2.2 wt pct less γ′ (strengthening precipitates) phase than in 1S alloy. The tensile strength of 1S alloy was about 2.2 pct more than 2H. The solution treatment of both alloys decreased the hardness, tensile and yield strengths by about 21 pct but ductility improved by about 17 pct. Fracture studies of both alloys showed the ductile mode of failure.     

Dispersion-Strengthened Copper Alloys with Useful Electrical and Mechanical Properties

Abstract

Dispersion-strengthened alloys have been made which combine a high level of tensile strength at temperatures up to at least 600°C with an electrical conductivity better than that of most precipitation-hardened copper alloys. The reverse gel precipitation process has been used to co-precipitate hydroxides which were then selectively reduced in hydrogen, consolidated under an atmosphere of pure argon, and finally hot-extruded to bar. Copper?3 vol.-% zirconia alloys were prepared in which all the particles were <150 nm dia., while copper–1·5 vol.-% thoria and copper–3 vol.-% thoria alloys were prepared with most particles <50 nm dia. Although the dispersion in the Cu–zirconia alloys was somewhat inferior to that obtained in the Cu–thoria alloys, useful properties were obtained. The Cu–zirconia alloys were as strong as the commercial alloy Cu–1 wt.-%Cr at 500°C and twice as strong at 600°C. There was little difference in the strength of a Cu–1·5 vol.-% thoria alloy and the Cu–zirconia alloys but the former was more ductile. The most interesting properties were obtained from Cu–3 vol.-% thoria alloys which exhibited an electrical conductivity in excees of 90% IACS at 20°C and tensile strength five times that of Cu–1%Cr at 600°C, even after annealing at 600°C for 1 h. The Cu–3 vol.-% thoria alloys were readily cold-worked, exhibited exceptional stability, and were resistant to recrystallization up to 900°C. Grain sizes were of the order of 1·5 μm for unalloyed copper, 1 μm for Cu–1·5% thoria, and 0·5 μm for Cu–3% zirconia or Cu–3% thoria. Grain growth was severely restricted by the dispersions.     

Processing and properties of sinter hardened Fe–Cr–Mo steels with admixed extra-fine nickel

Abstract

The processing and properties of chromium–molybdenum, powder metallurgy steels with admixed extra-fine nickel (XF Ni) were investigated. Prealloyed Fe–1·5Cr–0·2Mo powder was blended with different quantities of XF Ni, while a hybrid steel with lower Cr content was prepared by blending Fe–1·5Cr–0·2Mo and Fe–0·5Mo prealloyed powders, with additions of XF Ni and copper powders. These steels were compacted into different part shapes in order to evaluate the effect of part thickness on sinterhardening behaviour. These parts were also subjected to different cooling rates after sintering. This study showed that additions of XF Ni improve the compressibility, densification behaviour and mechanical properties of Cr–Mo steels. Furthermore, the properties of the hybrid steel were shown to be either equal to or greater than those of the reference material. Hardenability of all steels was sufficiently high such that part thickness was seen to have negligible impact. Higher cooling rates generally resulted in improved mechanical properties.     

HIGH-STRENGTH SINTERED IRON-BASE ALLOYS BY USING TRANSITION METAL CARBIDES

Abstract

A simple method of producing alloy steels by mixing, pressing, and sintering iron powder with carbides of transition metals is described. The carbides must have a high carbon content and be soluble in iron. These characteristics are found in the carbides of chromium, tungsten, molybdenum, and vanadium. Tensile strengths of ～800 N/mm² have been achieved in annealed specimens having carbide additions of 1–12 wt.-%, depending on the carbide. The additions produce steels with partly air-hardening properties.

The effects of concentration and particle size of the carbides, sintered density, sintering conditions, and cooling rate on mechanical properties have been determined. The alloys are not very sensitive to the sintering atmosphere. The effect of heat-treatment on the mechanical properties of Fe-Cr₃C₂ alloys is reported. A tensile strength >1300 N/mm² was observed with 4 wt.-% Cr₃C₂. Dilatometric measurements were conducted with different carbide concentrations and heating conditions to study the sintering process. The important process of homogenization was investigated by electron microprobe analysis.     

Supersolidus liquid phase sintering of high speed steels: Part 3: computer aided design of sinterable alloys

Abstract

Calculated multicomponent phase diagrams were used to identify high speed steel (HSS) type alloys having the potential to exhibit enhanced sinter ability. The requirement was for an extensive austenite + carbide + liquid phase field. Of the six tungsten and molybdenum based systems studied, Fe–14Mo–C + 4Cr–8Co systems were potentially the most promising. Appropriate compositions were water atomised and additional alloys prepared by blending annealed powders with graphite powders. Powders were compacted to green densities of about 70% theoretical and then vacuum sintered. Sinterability was assessed in terms of sintered densities and microstructures. Alloys containing Fe–13Mo–1·3C, Fe–14Mo–4Cr–1·3C, and Fe–14Mo– 8Co–4Cr–1·4C were sintered to full density at temperatures as low as 1170°C, 70–150 K lower than for existing HSSs. Sintering windows were 20– 30 K, a significant improvement on existing HSSs. As sintered microstructures consisted of angular M₆ C carbides dispersed in martensitic matrixes, which is typical for correctly sintered HSS. Heat treatment response and cutting performance for the sinterable grades were assessed and found to be comparable to existing HSS. The cutting performance of Fe–14Mo– 8Co–4Cr–1·4C tools at 45 and 52·5 m min^-1 was superior to both cast wrought M2 and T1 tools of identical geometry. Lower carbon contents resulted in an increase in sintering temperature and a reduction in the width of the sintering window. Higher carbon contents destroyed sinterability, since they led to the formation of M₂ C eutectic structures in the undersintered condition. Alloy sinterability was correlated to differential thermal analysis data obtained during heating of powders. The variations in sinterability with alloy composition are discussed with reference to phase diagrams; the degradation in sinterability observed at carbon contents above 1·4% is attributed to the presence of ternary eutectic phase fields. The commercial implications of the relationship between sinterability and alloy composition are discussed.     

SOME CHARACTERISTICS OF NICKEL-THORIA ALLOYS PREPARED BY HOT PRESSING IN CARBON DIES

Abstract

Fully dense nickel-thoria alloys, varying in ThO₂ content from 1·0 to 3·0 vol.-%, have been prepared by a powder-metallurgical method. The structures of the as-pressed alloys were examined and some of their mechanical properties measured. The effect on the yielding behaviour of the alloys of substituting MgO for ThO₂, and of varying the grain size of the matrix, has also been studied. An initial discontinuous yield is observed for as-pressed alloys and a strain-ageing effect for both as-pressed alloys and worked material. Decarburization has no influence on the initial discontinuous yield, but removes the strain-ageing effect. The strain-ageing behaviour of the alloys has been investigated and the interaction of carbon with dislocations demonstrated.     

High temperature properties of Cu–Cr–Zr alloys processed by conventional inverse extrusion of atomised powders and comparison with Conform consolidated powders

Abstract

Water atomised Cu–Cr–Zr alloy powders were consolidated by inverse warm extrusion and by the commercial continuous rotary extrusion method, Conform. Those alloys consolidated by inverse warm extrusion exhibited enhanced mechanical properties compared with their respective Conform extruded counterparts, when tested at both room and elevated temperatures. The processing parameters adopted in the inverse extrusion experiments resulted in products which retained enough amounts of solutes in solid solution, which in turn, led to improved mechanical properties after aging. Conversely, the excessive adiabatic heat generated in the Conform machine eliminated the saturation effect produced by rapid solidification, negating any possible further improvement on the mechanical properties by aging. The mechanical properties of an inverse extruded Cu–2.8Cr–0.39Zr (at.-%) alloy at temperatures above 450°C were higher than those strengths reported for Cu–Be alloys and comparable to that of Cu–Ta and Cu–Nb composites. Therefore, rapidly solidified Cu–Cr–Zr alloys can be possible candidates for replacing such alloy systems for high temperature applications.     

Leaner alloys for the PM industry

Abstract

Numerous lean alloy systems are now available to the PM parts manufacturer as potential lower cost solutions without sacrificing part performance. More recently, steels containing 0·3 and 0·5% prealloyed molybdenum have been introduced which can be tailored with reduced Ni and/or Cu additions to meet specific properties for use in press and sinter applications or as quench and temper grades. These reduced Mo prealloys complement the already familiar 0·85 and 1·5%Mo grades to provide a full range of prealloyed molybdenum steels. Another method to reduce susceptibility to market pricing has been through incorporating manganese, which is historically inexpensive yet highly beneficial to steel properties. Combining Mn with moderate levels of Mo in specially designed alloy grades provides a lean alternative to Ni and Cu containing hybrid alloy steels. This study will examine these lean alloys and explore where there may be opportunity to use them in place of traditional PM grades.     

SOME MECHANICAL PROPERTIES OF SAE 1045 STEEL JOINTS BONDED WITH SINTERED COMPACTS

Abstract

The physical and mechanical properties of plain steel (SAE 1045) butt joints, bonded with a sintered alloy as a filler material, are described. Sintered alloys were made from two types of iron powders–electrolytic and Swedish sponge– with various additions ranging from 7 to 20 wt.-% of an electrolytic copper powder, a prealloyed bronze powder (90% Cu+ 10% Sn), and a mechanically mixed elemental bronze powder.

The results showed that the tensile strength was not reduced as drastically as that of the copper-brazed joints, when the thickness of the bonding material (sintered alloy) was increased. The highest bond strength in tensile and fatigue testing was obtained with the sintered alloys comprising iron powder and 10 wt.-% pre alloyed bronze powder. The results indicate that there is a practical possibility of brazing steel using sintered compact as a filler material under a neutral or a reducing atmosphere.     

PM processing of elemental and prealloyed 6061 aluminium alloy with and without common lubricants and sintering aids

Abstract

A comparison has been made between compaction, sintering, microstructural and mechanical properties of the 6061 aluminium alloy prepared via premixed elemental (EL) and prealloyed (PA) powders (as received and degassed) with and without additions of sintering aids and various solid and/or liquid lubricants. Both EL and PA powders were cold pressed at different pressures, ranging from 250 to 770 MPa, and sintered under vacuum in the range 580–640^°C for 30–120 min. and then under pure nitrogen atmosphere for comparison. Vacuum degassing of the PA powder provided better compressibility and thus higher green densities than those for the as received PA or the premixed EL powder compacts pressed at compaction pressures ≥340 MPa. Near full sintered densities of , ～98%TD were obtained for both EL and PA 6061 Al alloys. Degassed PA Al with 0·6 wt-% paraffin wax (PW) or with only 0·12 wt-%Pb addition as sintering aid and no lubricant, and premixed EL with only 0·12 wt-%Pb addition and no lubricant gave the best optimum properties. It became apparent that additions of some solid lubricants such as lithium stearate (LS) and acrawax to both the premixed EL and PA powders provided reasonable green densities, but had deleterious effect on sintered densities and microstructures, particularly under vacuum sintering. Heating data curves during the sintering cycle, revealed formation of both transient and persistent liquid phases for the EL and mainly supersolidus liquid phase sintering (SLPS) mechanism for the PA. Tensile properties of the degassed, vacuum or nitrogen sintered PA Al alloy in T6 condition were higher than those of the equivalent alloy prepared by EL mixing with the former giving a tensile strength of 330 MPa and 6–8% elongation to failure, which are similar to those of the commercial (wrought) 6061 Al alloys.     

Contributors

Abstract

The chemistry of a high performance cast superalloy, ZhS6–K (Ni–10Cr–5Co–5W–5Al–3·5Mo–3Ti–0·2C–0·02B), was modified by slight reductions in carbon, titanium, and aluminium content and minor additions of niobium and hafnium. Two variants of the modified alloy chemistry with different boron contents (0·02 and 0·08 wt–%) were prepared by vacuum induction melting, argon atomization, and consolidation by hot isostatic pressing at three temperatures. It was observed that, unlike carbon, an increase in boron content did not promote the formation of continuous precipitates at the prior powder particle boundaries. Increased boron content narrowed down the consolidation temperature range and changed the morphology of γ′ particles from cuboidal to dendritic. Precipitation of an eutectic γ + γ′ structure and formation of continuous boride films at the grain boundaries severely degraded the mechanical properties of the high boron PM superalloy that was consolidated at a temperature marginally above the γ′ solvus. An optimum consolidation schedule was determined for the high boron alloy, which after a suitable heat treatment produced significant property improvement in stress rupture and tensile properties. PM/0416     

THE SINTERING OF URANIUM-CARBON-IRON ALLOYS IN THE PRESENCE OF A LIQUID PHASE

Abstract

The preparation of uranium mono carbide bodies containing ～1% open porosity and with a density of ～12·4 g/c.c. by cold compacting and sintering uranium/graphite mixtures is described. The effect of iron additions in producing a liquid phase during sintering has been studied, and it is shown that the addition of 10 wt.-% UFe₂ to the stoichiometric mixture of uranium and graphite raises the sintered density to ～13·1 g/c.c. and reduces the open porosity to ～0·5%. The mechanism of carbide formation and densification in the presence of a liquid phase is discussed.     

Effect of subsequent Hot Isostatic Pressing on mechanical properties of ASTM F75 alloy produced by Selective Laser Melting

Abstract

The Co-based alloy ASTM (Co – 28.5?wt.-% Cr – 6.3?wt.-% Mo) is widely used for medical implants, e.g. knee prostheses, and is commonly processed by investment casting. Selective laser (SLM) melting is supposed to be an efficient alternative for the production of individually designed knee implants regarding production time and production costs. The mechanical properties, in particular the fatigue strength, of the material have been studied in different states of the material. The mechanical properties of investment casted ASTM F75 and PM-SLM produced ASTM F75 were investigated. The focus in this study was on the PM-SLM material, the specimens were initially produced by selective laser melting and a part of the specimens were further processed by hot isostatic pressing (HIP). The PM-SLM material was mechanically tested in the as-SLM state as well as in the SLM+HIP state. It was found that the mechanical properties of the as-SLM material did not reach the level of the fatigue strength of as cast material. The post-densification treatment by HIP offers distinct improvements regarding the fatigue strength compared to the as-SLM material.     

开发Fe-Mn-Sn新烧结钢体系的研究

采用Mn作为合金元素,同时添加可进行液相烧结的元素Sn,形成Fe-Mn-Sn系合金。对由不同Mn、Sn含量组成的Fe-Mn-Sn系合金进行实验比较。实验结果表明,组分为Fe-6Mn-1Sn的合金具有较高的抗拉强度和硬度,其力学性能与适用于中等负荷的结构零件相当;组分为Fe-1Mn-0.25Sn的合金在延长保温时间的条件下可获得良好的延展性。     

Effect of alloying by transitional refractory metals on the microstructure and thermal stability of Al–5Zn–3Mg alloys

Abstract

The effect of additions of transitional refractory metals on the structure and properties of Al–Zn–Mg alloys, made by ingot and PM routes, was investigated. The strength of the ingot alloys especially is increased by scandium and zirconium. The modifying action of scandium inhibits recrystallisation and precipitation of the fine-grained coherent Al₃(Sc_1–xZr_x) phase. The effect is weaker in PM alloys where the ultra-high cooling rate during high pressure water atomisation produces the fine-grained structure. PM semi-products of the base composition Al–5Zn–3Mg and alloys without scandium are not recrystallised during heating to 500°C, whereas cast alloys of similar composition recrystallised on the hot extrusion stage at 400–450°C. Of the Sc alloys, Al–5Zn–3Mg–0·5Mn–0·7Zr–0·3Sc showed the highest strength (UTS?=?651 MPa, YS?=?596 MPa), whereas of the PM alloys without scandium Al–5Zn–3Mg–0·85Zr–0·22Cr–0·17Ni–0·15Ti alloy showed UTS?=?618 MPa and YS?=?553 MPa. At melt cooling rates of 10⁵–10⁶ K s^–1 the total content of transitional refractory metals must not exceed 1·5–1·7 wt-% and total content (Zn+Mg) should be <8 wt-% at a Zn/Mg ratio of 5:3.     

INFLUENCE OF IRON POWDER TYPE ON THE PROPERTIES OF SINTERED IRON AT VARIOUS DENSITY LEVELS

Abstract

The properties of various commercial and experimental iron powder types and of compacts made from them in the density range 6·8–7·87 kg/dm³ by single-pressing, double-pressing, and hot-forging techniques have been determined. It was shown that the ductility in all cases was more adversely affected than the tensile strength by the presence of porosity. However, it was also shown that at any particular density level or with a given processing schedule the mechanical properties varied widely, depending on the iron powder used. On the basis of the mechanical-property results, the powder types to be preferred at different density levels are indicated.     

On development of press and sinter Al–Ni–Mg powder metallurgy alloys

Abstract

The objective of this research was to initiate the development of powder metallurgy alloys based on the Al–Ni–Mg system. In doing so, binary (Al–Mg) and ternary (Al–Ni–Mg) blends were prepared, compacted and sintered using elemental and master alloy feedstock powders. Research began with fundamental studies on the sintering response of the base aluminium powder with additions of magnesium. This element proved essential to the development of a well sintered microstructure while promoting the formation of a small nodular phase that appeared to be AlN. In Al–Ni–Mg systems a well sintered structure comprised of α aluminium plus NiAl₃ was produced at the higher sintering temperatures investigated. Of these ternary alloys studied, Al–15Ni–1Mg exhibited mechanical properties that were comparable with existing commercial 'press and sinter' alloys. The processing, reaction sintering and tensile properties of this alloy were also found to be reproducible in an industrial production environment.