Utilisation of silicon rubber to characterise tool surface quality during die compaction

Abstract

A new methodology was developed to observe and measure tool wear and tool surface quality during the die compaction process. The newly developed method is a non-destructive test that relies on silicon rubber to transcribe the inner surface profile of the compaction die. After verification of the method, aluminium and iron alloy powders were compacted to quantify tool wear and tool surface quality with two die materials, tungsten carbide and tool steel. The tool surface quality was quantified by recording surface roughness of the die replicas on a surface profilometer.     

Influence of cooling and reheating on the evolution of copper rich liquid in high residual low carbon steels

Abstract

This study investigates some effects of austenite microstructure on processes leading to copper hot shortness. Low carbon steels containing 0˙55 wt-% copper were subjected to two thermal profiles in an infrared image furnace with attached confocal scanning laser microscope: hold at 1150°C for 60 s; hold at 1150°C for 60 s, quench to 400°C, reheat to 1150°C. Heat treatments were conducted in dried/deoxidised argon to image microstructures. Subsequent samples were oxidised in air. The oxide/metal interface was studied in a scanning electron microscope. Additional confocal scanning laser microscope experiments involved melting copper directly on the steel. After quench/reheat, austenite grain size decreased by a factor of ～1˙7 and grain boundaries were redistributed. Copper evolved during the first heating was no longer found at boundaries. Results from direct copper exposure reveal an apparent effect of boundary character on copper penetration rate. Possible mechanisms by which hot shortness is affected are discussed.     

Influence of atomising gas pressure on 63A solder powder in supersonic atomisation

Abstract

The atomising gas pressure is one of several important process parameters that affect the characteristics of the powder particles. The work analyses qualitatively the influence of the atomising gas pressure on 63A solder alloy fine powders. Also studied was the mechanism of the effect of the atomising pressure on the base of the air dynamics through the atomising 63A solder alloy experiment with different atomising pressures on the supersonic nozzle. The results indicate that 63A solder alloy fine powders may be attained, which can satisfy the SMT application requirement when the atomising gas pressure is at 0.7 MPa.     

A novel mathematical procedure to evaluate the effects of surface topography on the interfacial state of stress. Part I: Verification of the method for flat surfaces

A mathematical procedure is developed to utilize the complementary energy method, by minimization, in order to obtain an approximate analytical solution to the 3D stress distributions in bonded interfaces of dissimilar materials. The stress solutions obtained predict the stress jumps at the interfaces, which cannot be captured by current FEA methods. As a novel method, the penalty function is used to enforce the displacement boundary conditions at the interfaces. Furthermore, the mathematical procedure developed enables the integration of different interfacial topographies into the solution procedure. In order to incorporate the effects of surface topography, the interface is expressed as a general surface in Cartesian coordinates, i.e. F (x, y, z) = 0. In this paper, the flat interface problem, i.e. y = 0 surface is considered for verification of the method by comparison with the FEA method. A comparison of the results reveals our new mathematical procedure to be a promising and efficient method for optimizing interface topographies.     

Effects in Surface Free Energy of Sputter-Deposited VNx Films

Vanadium nitride (VN _x ) thin films have attracted much attention for semiconductor integrated circuit (IC) packaging molding dies, and forming tools due to their excellent hardness and, thermal stability. VN _x thin films with VN_0.45, VN_0.83, VN_1.22, VN_1.73, VN_2.06 were prepared using a radio frequency (RF) sputter technique. The experimental results showed that the contact angle at 20°C increases with increasing nitrogen content of the VN _x films, to 101.4° corresponding to VN_1.73 and then decreased. In addition, the contact angles decreased with increasing surface temperature, because an increase of the surface temperature disrupts the hydrogen bonds between water and the films and the water gradually vaporizes. The total surface fee energy (SFE) at 20°C decreased with nitrogen content of the VN _x films to 29.8 mN/m (VN_1.73) and then increased. This is because a larger contact angle means weaker hydrogen bonding which results in a lower SFE. The polar SFE component had the same trend as the total SFE, but the dispersive SFE component had the opposite trend. The polar SFE component is also lower than the dispersive SFE component. This is because hydrogen bonds are polar. The total SFE, dispersive SFE and polar SFE of the VN _x films all decrease with increasing surface temperature. This is because with increasing temperature, water evaporates from the surface, disrupting hydrogen bonds and hence increasing surface entropy. The film roughness has an obvious effect on the SFE and there is tendency for the SFE to increase with increasing film surface roughness. As a result the SFE and surface roughness can be expressed in terms of a simple ratio function.     

Classification of above burden profile using SOM and k-means

Abstract

Blast furnace operators mostly depend on the measurements taken from the inputs and outputs in the control of the process to interpret the information available for vertical and radial distribution of variables, such as, heat load on the boundary and the distribution of the gas across the section of the furnace. Gas distribution inside the furnace is largely dependent on the distribution of the burden inside the furnace and its estimation is a challenge to the blast furnace operators. However, the measurement from the above burden probes gives some insight to the radial gas distribution in the shaft. Design of methods for automatic classification of above burden probe (ABP) profile is thus warranted. The self-organising map (SOM) is an excellent tool in the exploratory phase of data mining. It projects input space on prototypes of a low dimensional regular grid that can be effectively utilised to visualise and explore properties of the data. When the number of SOM units is large, to facilitate quantitative analysis of the map and the data, similar units need to be grouped, i.e. clustered. In the present investigation, a model for classification, visualisation and interpretation of ABP profiles has been developed by two stage procedure, i.e. SOM followed by k-means clustering. This classifier has the potential to be a useful tool for operator guidance in daily practice.     

Structural stability and non-catalytic nucleation inhibition effect of Si–Zr–B mould coating on undercooled superalloy melt

Abstract

The investment moulding technique was first adopted to prepare a SiO₂–ZrO₂–B₂O₃ (Si–Zr–B) substrate layer on the inner surface of the mould, by employing SiO₂ glass dust and ZrO₂ powder, SiO₂–ZrO₂ sol, and analytical grade H₃BO₃ as refractory material, binder, and softening agent, respectively. Then using sol–gel processing, seven layers of Si–Zr–B film of the same formula as the aforementioned Si–Zr–B substrate layer were compounded with the substrate layer step by step. After glassing treatment at 850°C for 60 min, this film transformed into a glass lined coating. It was shown from X-ray diffraction analysis that, after holding it at a temperature of 1500°C for 30 min, the amount of crystallinity in the Si–Zr–B coating was about 1–3% (vol.-%). Finally, the undercooling experiment showed that a large undercooling (up to 140 K) was achieved in a DD3 (Ni–Cr–Mo–Al–Ti–Co–W) single crystal superalloy melt in this coated mould. So it is concluded that a Si–Zr–B coating has got a good structural stability at high temperature and provides ideal non-catalytic nucleation inhibition for an undercooled superalloy.     

Effects of different metals on adhesive wear behaviour of alloy surface produced by TIG process

Abstract

Low carbon steel surfaces were alloyed with composite powders using the tungsten inert gas welding method. After the alloying process, the effects of cladding surface on the microstructural characteristics and adhesive wear of the alloyed samples were examined. The sliding wear behavior of samples was investigated in a block on ring apparatus under the loads of 20, 40, 60 and 80 N respectively. In the experimental investigation, a low carbon steel surface was alloyed with austenitic stainless steel powder and austenitic stainless steel powder mixed with 4·5% Co, Mo and Ti particles respectively. Following surface alloying, conventional characterisation techniques, such as optical microscopy, scanning electron microscopy, energy dispersive spectrograph and X-ray diffraction, were used to study the microstructure of the alloyed zone. Examination of the microstructure revealed the presence of M₂₃C₆ carbides, solid melt phases and intermetallic phases, such as Ni₃Ti, depending on the alloying element in the composite. As the amount of the reinforcing material increased, the saturation rates for the samples decreased, while their hardness increased. The adhesive abrasion tests conducted revealed that temperature input plays a significant role on the microstructure characteristics, which positively affected the adhesive abrasion values of the samples. Consequently, the tungsten inert gas welding method was successfully used for the surface alloying of low carbon steels.     

1st Mediterranean Conference on Heat Treatment and Surface Engineering

Abstract

Energy and the environment are not only receiving mass public attention, but are also indisputably the main drivers for the development of present day scientific, industrial, economic and social progress. However, anyone attempting to review these topics faces two huge problems: the overwhelming volume of often conflicting information and the rapidly evolving national, international and global situation. Thus, the survey presented here, with heat treatment and surface engineering in mind, is a selection of ideas, discussion material and data that is designed to trigger focused discussion and substantive contributions.