Lauri Kollo

Reactive Sintering of ZrC-TiC Composites

Inherently, zirconium carbide (ZrC) suffers from low fracture toughness (~3 MPa*m1/2) and excessive porosity when sintered in vacuum. One way to improve ZrC’s sinterability and fracture toughness is the addition of binder metal or other carbides to increase densification. Using mechanical activated synthesis (MAS) to homogenously mix ZrC and titanium carbide (TiC) powders, followed by sintering at 1900 °C, produces a ZrC-TiC composite with hardness and fracture toughness at 20 GPa & ~7 MPa*m1/2, respectively. 80ZrC-20TiC (wt%) gave the highest fracture toughness value compared to other ratios. Varying TiC ratio from 20 - 50 wt% does little to affect mechanical hardness or densification of the composite. However, fracture toughness appears to increase marginally with decreasing TiC concentration down to ~20 wt%.

Heat Treatment of Ultrafine Grained AA 6061 Consolidation by Equal Channel Angular Pressing

During the last decade Equal Channel Angular Pressing (ECAP) has emerged as a widely known procedure for the fabrication of ultrafine grained metals and alloys. This review examines recent developments related to the use of ECAP for grain refinement. In the current study the part of capsules wrapper for powder material to be compressed where the powder AA6061 was wrapped in copper sheet and heated at a temperature of 400 OC in hot pressed under the pressure of 400 MPa. Afterward the powder in solid condition was cooled in the air and then does analysis characterization. The sample results of AA6061 are ECAP as is and heat treatment with type Anneal and Artificial Aging (T6) where heat treatment is heated at a temperature of 530 °C for 1 h followed by heating at a temperature of 100 °C for one day and the other for heating at a temperature of 415°C for 2.5 hours followed by heating at a temperature of 177 °C for 8 hours. This paper explains the characteristics of each sample where analyses are based on the mechanism of properties to determine how much change of mechanical properties and microstructure. Heat treatment effect on grain coarsening so that the mechanical properties can be engineered.

Heat Treatment of Ultrafine Grained High-Strength Aluminum Alloy

Aluminum is one of the nonferrous metals with very wide applications. It has unique properties such as light weight and it is ductile has additionally, lower melting point compared to iron. Equal Channel Angular Consolidation (ECAC) is manufacturing method to produce alloys with high strength by consolidation at elevated temperatures. ECAC method can produce a fine grain and combined with oxide inclusion from particle surfaces, high strength. This research will examine the applicability of Equal Channel Angular Consolidation to incorporate aluminum Al 7075 series powder at a temperature of 400OC under pressure of 400 MPa. The effects of heat treatment regimes on grain size of the ECAC samples are observed. The results show hardness of 7075 Aluminum series after ECAC process reaching 120 HV10 and decreases down to 110 HV10 after T6 heat treatment. Hardness further decreases after annealing process, down to 104 HV10. Decline in hardness is accompanied with the increased grain size, which accompanies increased ductility.

Influence of Pressurized Sintering on Performance of TiC-Based Cermets

This paper discusses the effect of advanced sintering technologies – sinter + hot isostatic pressing (HIP) and sinter/HIP on the performance of TiC-based cermets. The performance was evaluated by strength (transverse rupture strength), adhesive wear resistance and durability. Adhesive wear was performed by a turning method (turning of mild steel at low speed) while durability was evaluated by functional testing – wear of tools during blanking of sheet metal. It was found that sinter/HIP ensures a higher positive effect than sinter + HIP in different cycles.

Nanoparticulate Reinforced Aluminum Alloy Composites Produced by Powder Metallurgy Route

High energy planetary ball-milling was used to effectively disperse 3, 6 and 9 wt. % multiwall carbon nanotubes (MW-CNTs) into commercially available aluminum alloys (Al6061, AlMg5, S250 and S790). Composite bulks were manufactured by uniaxial hot pressing. For the Al6061- CNT composites, standard heat treatments (T4, T5 and T6) were performed and their influence on the structural evolution (grain coarsening, CNT reaction) and hardness was recorded. Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Raman spectroscopy were used to characterize the produced composites. The study shows that CNTs can be effectively mixed with high-strength aluminum alloys. Up to 5 fold increase in hardness was achieved compared to unreinforced alloys ranging up to 390 HV20 for the S250 alloy with 6 wt. % of MW- CNTs. The applied standard heat treatments did not lead to any improvements of the mechanical properties. The developed nanocomposite materials could find applications where high hardness of aluminum is needed, or in functionally graded composites.

Structure and Magnetic Properties of NdFeB Powder Prepared by Hydrogen Decrepitation and High-Energy Ball Milling

An ingot of NdFeB alloy was disintegrated by hydrogen decrepitation (HD). High-energy ball milling technique with hard metal milling elements and balls was employed to refine HD powders down to particle size optimum for magnet processing. The experiments were performed according to experimental plan to optimize the milling parameters regarding particle size, contamination and magnetic properties of the powder. The effect of milling time, speed of rotation, ball-powder weight ratio (BPR) and amount of wet agent was investigated. The highest influence was shown to be from attritor speed of rotation, ball-to powder ratio and combined effect of milling wet agent and rotating speed. Unified parameter of estimated number of total ball impacts was calculated, which allows predicting the final particle size of the powder at different milling speeds. Magnetic moments of powders were measured.

Surface Fatigue of Al-Metal Matrix Composites at Impact Loading

Aluminium 6061 has proven to be a suitable alloy as a basis for producing metal matrix composites (MMC). These MMCs have a low specific weight combined with a relatively good specific stiffness and high specific strength. The hardness and compressive strength of Al composites can be increased by reinforcing bulk material with nano particles. However the ductility of such alloys is relatively low, therefore one of the applications for such light alloys could be wear applications. In many wear conditions such as erosive or abrasive wear at normal impact angles the surface wear resistance plays a significant role. The surface fatigue properties have not been widely studied for such nanoparticle reinforced aluminium composites. The nano-reinforced composite materials were produced by means of high-energy milling (HEM) of nano-sized reinforcement particles together with a metallic matrix powder, followed by hot pressing. By utilizing up to 6 wt% multiwalled carbon nanotubes (MWCNT) as reinforcement the hardness of Al6061 MMC has been increased from 45 HV10 up to 317 HV10, compressive yield strength from 58 MPa up to 660 MPa and indentation modulus from 60 GPa up to 90 GPa compared to hot pressed Al6061. Surface fatigue tests were conducted at impact (dynamic) loading conditions using a hardened steel sphere as indenter. The Wöhler-like curves are plotted to estimate the surface fatigue. The surface fatigue indents were photographed by the aid of light optical microscopy (LOM) and analysed by image analysis software and optical profilometry (OP).

Effect of Sinter/HIP Technology on Properties of TiC-NiMo Cermets

The present work is a study on the argon gas pressure effects of Sinter/HIP sintering on microstructure and strength of different grades of TiC-NiMo cermets. Titanium carbide in the composition of different grades of TiC-NiMo cermets was ranged from 40 to 80 wt.% and the ratio of nickel to molybdenum in the initial powder composition was 1:1, 2:1 and 4:1 respectively. On the sintered alloys, the main strength characteristic, transverse rupture strength (TRS) and erosion wear resistance were measured. Furthermore, the microstructure parameters of some alloys were measured and the pressure effect on pore elimination was evaluated. All the results were compared with common, vacuum sintered alloys. The TRS values of TiC-NiMo cermets could be considerably improved by using Sinter/HIP technique, for high-carbide fraction alloys and for alloys sintered at elevated temperatures. The results provide new possible application fields for Sinter/HIP-ed TiC cermet materials to areas where, in addition to wear performance, higher strength properties are demanded.