Papers by Keyword: Master Alloy

Abstract: The application of “masteralloys” as alloying carriers in Powder Metallurgy (PM) steels enables the introduction of highly oxygen‑sensitive alloying elements for advanced PM‑steels, by using a tailored liquid phase. The characteristics of the liquid and its interaction with the iron base powder are determining factors for final microstructure and dimensional behaviour. In this study, theoretical calculations and experimental findings are presented for the masteralloy systems Fe_Mn_Si_C, Fe_Cr_Si_C and Fe_Mn_Cr_Si_C. Lowered melting temperatures and narrow melting temperature intervals could be achieved. The interaction between Fe base material and the masteralloys was studied by infiltration and DTA experiments. It was found that by adjusting the C and Si content in the masteralloy, liquids with widely varying properties could be obtained. This might be a key for tailoring microstructures, properties and dimensional stability of advanced PM‑steels.

Abstract: In real industrial environment there is always a difference between ideal theoretical condition and real production condition which bears the risk of producing defective or low quality parts. Getting closer to this ideal situation requires more effort and investment which tends to increase the production cost. In the P/M production lines, the sintering stage is one of the most critical processes. Maintaining an open continuous sintering furnace in an ideal condition is a challenge, and this issue gets more pronounced when using alloy powder containing oxygen-sensitive elements such as Cr or Mn which provide good hardenability at low cost but on the other hand form stable oxides that weaken the sintering contacts if they are not reduced properly. In the present study, using a carbon master alloy as a sintering enhancer in the sintering process of Cr-Mo alloyed powder compacts has been investigated. For clearly depicting the effect of carbon master alloy addition on carbon dissolution and deoxidation, sintering was done in argon as inert atmosphere to avoid other reducing agents such as H₂. The physical and mechanical properties of the sintered specimens were investigated, and thermal chemical analysis by DIL/MS and carbon/oxygen measurements were performed. The experiments showed that adding iron-carbon masteralloys promote the sintering processes such as reduction of oxides and carbon dissolution in the early stages of sintering, resulting in better properties after final sintering.

Abstract: P-doped γ-Al₂O₃ was found to be a potent substrate to nucleate primary silicon whilst good modification of the eutectic matrix is retained during solidification of hypereutectic Al-Si alloys. On using P-doped γ-Al₂O₃ could be a perfect and clean source of P without additional impurities. The optical micrographs show that the morphologies of primary silicon crystals in solidification of Al-18Si alloy are changed from irregular coarse morphologies to fine regular particles. The average particle size of primary Si decreased from 52 μm to 25 μm and 22 μm in adding P-doped α-Al₂O₃ and P-doped γ-Al₂O₃ respectively. It was clear that P-doped γ-Al₂O₃ led to good refinement of primary Si and the modification effect on eutectic Si was retained in solidification of commercial purity Al-18Si alloy. Adding P-doped γ-Al₂O₃ give a good primary Si refinement to Al-18Si alloy if compared with the addition of P and using finer P doped γ-Al₂O₃ powder give narrower particle size range similar to that of adding P.

Abstract: Master alloys are used in the metals industry to control chemical composition and to help to achieve a particular microstructure or promote growth of desired phases. This study reports on making a Al₃Nb containing aluminium (Al) - niobium (Nb) master alloy by solid-liquid reaction processing, where solid Nb particles are added to the liquid Al. Nb react with Al to form in-situ Al₃Nb. The in-situ formed Al₃Nb particles were facet and polygonal in shape. The three dimensional analysis revealed that the outer surface of the partially reacted Nb was covered with faceted Al₃Nb particles. The different nature and morphologies of the in-situ phases that were produced were determined using SEM, EDX, XRD and extraction techniques. A mechanism for the observed microstructural difference is discussed.

Abstract: Master alloys are used in the metals industry to control chemical composition and to help to achieve a particular microstructure or promote growth of desired phases. This study reports on making a Al₃Nb containing aluminium (Al) - niobium (Nb) master alloy by solid-liquid reaction processing, where solid Nb particles are added to the liquid Al. Nb react with Al to form in-situ Al₃Nb. The in-situ formed Al₃Nb particles were facet and polygonal in shape. The three dimensional analysis revealed that the outer surface of the partially reacted Nb was covered with faceted Al₃Nb particles. The different nature and morphologies of the in-situ phases that were produced were determined using SEM, EDX, XRD and extraction techniques. A mechanism for the observed microstructural difference is discussed.

Abstract: Ti₆₀(Ni_xCu_40-x)₄₀ x = 5 - 40 at% ternary alloys were prepared by arc-melting followed by a centrifugal casting into a wedge-shaped copper mould in order to examine glass forming of these compositions. Microstructure of the master alloys and wedge-shaped samples were studied. Among the master alloys, which solidified under non-equilibrium conditions, the sample with 15 at% Ni content displayed clear eutectic structure and its wedge-shaped sample had the finest structure but still crystalline. Microstructure of the other compositions was far from amorphous state.

Abstract: Powder metallurgy (PM) permits to obtain titanium alloys with properties and microstructures close to ingot metallurgy products. However, residual porosity is normally present in the products produced by the PM route of powder pressing and sintering (P&S)\, and this needs to be reduced by using post-sintering process step such as hot isostatic pressing (HIP) and forging. In this study, the microstructural and mechanical property changes caused by HIP of samples of two alloys, near-α Ti-3Al-2.5V alloy and α+β Ti-6Al-4V, produced by P&S route were investigated. Two types of powders were utilised: prealloyed powders and blend of elemental titanium powder and master alloy powder. Four conditions defined by HIP temperature, pressure and time were used to HIP the sintered samples with two geometries. The results show that, independent of the HIP conditions used, HIP increased the relative density of the samples to approximately 97.5% and their hardness by 30-50 HV depending on the HIP condition. However, HIP at 1000°C changes the fracture mode of the sintered samples from ductile to brittle.

Abstract: AlTiC master alloys have been prepared by Contact Reaction Method（CRM）.X-ray diffraction，SEM and EDS were used to analyse the AlTiC master alloys. It showed that morphology and distribution of TiC and Al3Ti particle have correspondingly changed with the transformation of temperature. As a result, the change in morphology and distribution of TiC and Al3Ti particle has considerably affected the gain refining performance of AlTiC master alloys. The result showed that it had excellent grain refining performance for commercially pure aluminum in 800°C.

Abstract: Since low alloyed sintered steels were introduced in the market of the structural parts, we have followed the evolution of a material with poor mechanical properties and any uniformity (in the sense of reproducibility) to materials that today are produced with high reliability and performance. The working efficiency could be equivalent in many cases with the best wrought steel, and maintaining a good margin in terms of cost and competitively. In this paper a complete review of the topic is accomplished, from the early times when the first parts were made by plain iron or iron-carbon, going through the different alloying systems: Fe-Cu, Fe-P, Fe-Cu-Ni-Mo, and more recently Fe-Cr-Mo and Fe-Mn. The development in processing routes has been considered too. The main milestones in the field of new alloying systems have been: 1) the introduction of Cu in 60-70’s, 2) the new complex systems with Cu-Ni-Mo in the 80’s and 3) the introduction of alloying elements with high oxygen affinity (in the late 90’s). Regarding the milestones in processing could be considered: 1) the development of new mixing procedures, 2) the warm compaction and high velocity compaction, 3) the improvements in sintering control and high temperature sintering. Several decades of research and innovation, acting on the processing system (mixing, pressing, sintering, post-sintering operations,…) and on the alloying system (from the earliest times with plain iron to complex systems used today), has allowed us to have a highly competitive materials, in terms of performance, and processes in terms of cost. The future is still open to new developments.

Abstract: AlTiC master alloys have been prepared by Contact Reaction Method（CRM）.X-ray diffraction，SEM and EDS were used to analyses the AlTiC master alloys. It showed that morphology and distribution of TiC and Al3Ti particle have correspondingly changed with the change of the size of powder. As a result, the change in morphology and distribution of TiC and Al3Ti particle has considerably affected the gain refining performance of AlTiC master alloys. The result showed that: when the grain size of Ti is much smaller, the effect of refinement is much better.