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1 – 10 of 143
Article
Publication date: 20 March 2009

C. Zhang, Y. Huang, Y. Liu, S. Wang and X. Zhang

The purpose of this paper is to study the isothermal and nonisothermal crystallisation kinetics of pure polypropylene (PP), 1 kGy pre‐irradiated PP and 1 kGy…

Abstract

Purpose

The purpose of this paper is to study the isothermal and nonisothermal crystallisation kinetics of pure polypropylene (PP), 1 kGy pre‐irradiated PP and 1 kGy pre‐irradiated PP/syndiotactic 1,2‐polybutadiene (s‐1,2 PB) (90/10) blends by differential scanning calorimetry.

Design/methodology/approach

The Avrami equation, modified Avrami equation, Ozawa equation and the treatment by combining the Avrami and Ozawa equation were used to analyse the isothermal and nonisothermal crystallisation of various samples.

Findings

The s‐1,2 PB acted as a heterogeneous nucleation agent during the crystallisation of the PP/s‐1,2 PB blends and accelerated the crystallisation rate. The Avrami exponent n of the blends implied that the isothermal crystallisation kinetics of the blends followed a three‐dimensional growth via heterogeneous nucleation. The modified Avrami equation was limited to describe the nonisothermal crystallisation process of pure PP and 1 kGy pre‐irradiated PP, but it was successful for the blends. The treatment by combining the Avrami and Ozawa equation described appropriately the nonisothermal crystallisation process and obtained the kinetic parameter F(T) with specific physical meaning. The crystallisation activation energy for isothermal crystallisation and nonisothermal crystallisation of the blends was reduced due to the s‐1,2 PB acting as a heterogeneous nucleating agent during the crystallisation of the blends and accelerating the crystallisation rate.

Research limitations/implications

The Avrami equation, modified Avrami equation, Ozawa equation and the treatment by combining the Avrami and Ozawa equation were compared for analysis of the isothermal and nonisothermal crystallisation of samples. The crystallisation activation energy for isothermal crystallisation and nonisothermal crystallisation was also calculated according to the Arrhenius and the Kissinger method.

Practical implications

The fundamental research on the crystallisation properties of PP/s‐1,2‐PB blends is essential to understand the mutual effects of two components on their crystallisation mechanisms, facilitating to improve the mechanical properties of the final materials.

Originality/value

The isothermal and nonisothermal crystallisation behaviours of PP/s‐1,2 PB blends, especially pre‐irradiated PP/s‐1,2 PB blends, have not been studied systematically yet, though PP/s‐1,2 PB blends were promising materials in terms of both PP toughening and the application of s‐1,2 PB thermal plastic elastomer.

Details

Pigment & Resin Technology, vol. 38 no. 2
Type: Research Article
ISSN: 0369-9420

Keywords

Article
Publication date: 27 November 2018

Fuda Ning, Yingbin Hu and Weilong Cong

The purpose of this paper is to identify if the implementation of ultrasonic vibration in laser engineered net shaping (LENS) process can help to reduce internal…

493

Abstract

Purpose

The purpose of this paper is to identify if the implementation of ultrasonic vibration in laser engineered net shaping (LENS) process can help to reduce internal weaknesses such as porosity, coarse primary TiB whisker and heterogeneous distribution of TiB reinforcement in the LENS-fabricated TiB reinforced Ti matrix composites (TiB-TMC) parts.

Design/methodology/approach

An experimental investigation is performed to achieve the results for comparative studies under different fabrication conditions through quantitative data analysis. An approach of microstructural characterization and mechanical testing is conducted to obtain the output attributes. In addition, the theoretical analysis of the physics of ultrasonic vibration in the melting materials is presented to explain the influences of ultrasonic vibration on the microstructural evolution occurred in the part fabrication.

Findings

Because of the nonlinear effects of acoustic streaming and cavitation induced by ultrasonic vibration, porosity is significantly reduced and a relatively small variation of pore sizes is achieved. Ultrasonic vibration also causes the formation of smaller TiB whiskers that distribute along grain boundaries with a homogeneous dispersion. Additionally, a quasi-continuous network (QCN) microstructure is considerably finer than that produced by LENS process without ultrasonic vibration. The refinements of both reinforcing TiB whiskers and QCN microstructural grains further improve the microhardness of TiB-TMC parts.

Originality/value

The novel ultrasonic vibration-assisted (UV-A) LENS process of TiB-TMC is conducted in this work for the first time to improve the process performance and part quality.

Details

Rapid Prototyping Journal, vol. 25 no. 3
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 14 September 2011

P. Zak, J. Lelito, J. Suchy, W. Krajewski, K. Haberl and P. Schumacher

The aim of this paper was to determine fitting parameters in grain density of the magnesium primary phase function in AZ91/SiC composite heterogeneous nucleation model…

Abstract

The aim of this paper was to determine fitting parameters in grain density of the magnesium primary phase function in AZ91/SiC composite heterogeneous nucleation model. Nucleation models have parameters, which exact values are usually not known and sometimes even their physical meaning is under discussion. Those parameters can be obtained after statistical analyze of the experimental data. Specimens of fourteen different composites were prepared. The matrix of the composite was AZ91 and the reinforcement was SiC particles. The specimens differs in SiC particles size (10 μm, 40 μm, 76 μm) and content (0 wt.%, 0.1 wt.%, 0.5 wt.%, 2 wt.%, 3.5 wt.%). They were taken from the region near to the thermocouple, to analyze the undercooling for different composites and its influence on the grain size. The specimens were polished and etched. The mean grain size for each specimen was measured. Specific undercooling for each composite was found from characteristic points on cooling rate curve. Microstructure and thermal analyze gave set of values that connect SiC particles content, their size and alloy undercooling with grain size. Those values were used to approximate nucleation model adjustment parameters. Obtained model can be very useful in modelling composites microstructure.

Details

World Journal of Engineering, vol. 8 no. 3
Type: Research Article
ISSN: 1708-5284

Keywords

Article
Publication date: 1 September 1995

Young Kag Kim and Sang Soo Kim

We present the equations for condensation in cooled upward laminar flowin tubes and consider their solution for low vapour concentrations andvariable vapour‐gas…

Abstract

We present the equations for condensation in cooled upward laminar flow in tubes and consider their solution for low vapour concentrations and variable vapour‐gas thermodynamic properties. We treated the full problem, including coupling with the aerosol size distribution, by using the PSI‐CELL (Particle Source in Cell) method. The particle trajectories start from the point where the particles are generated homogeneous nucleation. Particle size distribution and vapour scavenging by particles are obtained in forced convection and mixed convection regions. Calculations were also conducted with respect to tube diameters.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 5 no. 9
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 18 November 2013

Shu Li and Ping Wu

The aim of the present work is to study the effect of processing conditions on solidification path and resultant microstructure and further predict the solidification…

Abstract

Purpose

The aim of the present work is to study the effect of processing conditions on solidification path and resultant microstructure and further predict the solidification behavior of gas-atomized Sn-5mass%Pb droplets.

Design/methodology/approach

Combined with previous models for in-flight droplet nucleation and non-equilibrium solidification, a simulation method is applied to four typical containerless solidification conditions with helium, nitrogen or argon gas at two different gas jet velocities, in the presence of 10 or 500 ppm oxygen. The simulation outputs distribution of primary dendrite composition, tip velocity and tip radius with radial distance from the nucleation point, and the fraction solid at the end of recalescence and the post-recalescence duration. Both surface and internal nucleation are considered. The possible dendritic fragmentation in the post-recalescence stage is also discussed.

Findings

Result indicates that dendritic fragmentation is not likely to occur in droplets solidifying along the paths considered in the simulation.

Originality/value

The simulation method applies to any droplet-based solidification process for which droplet cooling schedule is known and thus provides a scientific basis for powder quality assurance.

Details

Multidiscipline Modeling in Materials and Structures, vol. 9 no. 4
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 1 December 1996

M. Wünsche, H. Meyer and R. Schumacher

This paper reports on a method for in‐situ observation of the morphology and stability of electrochemically generatedmetal layers. This information is obtained by…

328

Abstract

This paper reports on a method for in‐situ observation of the morphology and stability of electrochemically generated metal layers. This information is obtained by comparing topographical and kinetic data. The method is based on coulometric, microgravimetric and optical measurement performed in situ on vertically growing electrodes. Measurements are obtained simultaneously from the same surface area.

Details

Circuit World, vol. 22 no. 3
Type: Research Article
ISSN: 0305-6120

Keywords

Article
Publication date: 25 January 2021

Xu Han, Xiaoyan Li, Peng Yao and Dalong Chen

This study aims to investigate the interfacial microstructures of ultrasonic-assisted solder joints at different soldering times.

Abstract

Purpose

This study aims to investigate the interfacial microstructures of ultrasonic-assisted solder joints at different soldering times.

Design/methodology/approach

Solder joints with different microstructures are obtained by ultrasonic-assisted soldering. To analyze the effect of ultrasounds on Cu6Sn5 growth during the solid–liquid reaction stage, the interconnection heights of solder joints are increased from 30 to 50 μm.

Findings

Scallop-like Cu6Sn5 nucleate and grow along the Cu6Sn5/Cu3Sn interface under the traditional soldering process. By comparison, some Cu6Sn5 are formed at Cu6Sn5/Cu3Sn interface and some Cu6Sn5 are randomly distributed in Sn when ultrasonic-assisted soldering process is used. The reason for the formation of non-interfacial Cu6Sn5 has to do with the shock waves and micro-jets produced by ultrasonic treatment, which leads to separation of some Cu6Sn5 from the interfacial Cu6Sn5 to form non-interfacial Cu6Sn5. The local high pressure generated by the ultrasounds promotes the heterogeneous nucleation and growth of Cu6Sn5. Also, some branch-like Cu3Sn formed at Cu6Sn5/Cu3Sn interface render the interfacial Cu3Sn in ultrasonic-assisted solder joints present a different morphology from the wave-like or planar-like Cu3Sn in conventional soldering joints. Meanwhile, some non-interfacial Cu3Sn are present in non-interfacial Cu6Sn5 due to reaction of Cu atoms in liquid Sn with non-interfacial Cu6Sn5 to form non-interfacial Cu3Sn. Overall, full Cu3Sn solder joints are obtained at ultrasonic times of 60 s.

Originality/value

The obtained microstructure evolutions of ultrasonic-assisted solder joints in this paper are different from those reported in previous studies. Based on these differences, the effects of ultrasounds on the formation of non-interfacial IMCs and growth of interfacial IMCs are systematically analyzed by comparing with the traditional soldering process.

Details

Soldering & Surface Mount Technology, vol. 33 no. 4
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 15 October 2018

Xin Zhao, Bo Dong and Weizhong Li

The freezing phenomenon of a falling droplet is a frequently encountered phenomenon in various applications, such as spray crystallization, hail formation and artificial…

Abstract

Purpose

The freezing phenomenon of a falling droplet is a frequently encountered phenomenon in various applications, such as spray crystallization, hail formation and artificial snowmaking. Therefore, this paper aims to understand the freezing processes of a falling droplet without and with initial horizontal velocity in a cold space.

Design/methodology/approach

The freezing processes of a falling droplet were characterized using a modified enthalpy-based lattice Boltzmann method.

Findings

The temperature field, streamlines and freezing process of the falling droplet were investigated and analyzed. The lower part of the droplet was frozen earlier than the upper part. The freezing trend slowed down in the later stage of the freezing process. The droplet shape was related to the initial vertical velocity, nucleation temperature and initial horizontal velocity.

Originality/value

A modified enthalpy-based lattice Boltzmann method is proposed. In the model, the improved pseudo-potential model is used and the radiation is considered. This method was firstly used to simulate the freezing process of a falling droplet. By examining these freezing processes in detail, the freezing trend and the effect factors of droplet deformation and freezing time were obtained, respectively.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 28 no. 10
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 23 October 2018

Jingfu Liu, Behrooz Jalalahmadi, Y.B. Guo, Michael P. Sealy and Nathan Bolander

Additive manufacturing (AM) is revolutionizing the manufacturing industry due to several advantages and capabilities, including use of rapid prototyping, fabrication of…

911

Abstract

Purpose

Additive manufacturing (AM) is revolutionizing the manufacturing industry due to several advantages and capabilities, including use of rapid prototyping, fabrication of complex geometries, reduction of product development cycles and minimization of material waste. As metal AM becomes increasingly popular for aerospace and defense original equipment manufacturers (OEMs), a major barrier that remains is rapid qualification of components. Several potential defects (such as porosity, residual stress and microstructural inhomogeneity) occur during layer-by-layer processing. Current methods to qualify AM parts heavily rely on experimental testing, which is economically inefficient and technically insufficient to comprehensively evaluate components. Approaches for high fidelity qualification of AM parts are necessary.

Design/methodology/approach

This review summarizes the existing powder-based fusion computational models and their feasibility in AM processes through discrete aspects, including process and microstructure modeling.

Findings

Current progresses and challenges in high fidelity modeling of AM processes are presented.

Originality/value

Potential opportunities are discussed toward high-level assurance of AM component quality through a comprehensive computational tool.

Details

Rapid Prototyping Journal, vol. 24 no. 8
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 26 August 2014

Guokui Ju, Fei Lin, Wenzhen Bi, Yongjiu Han, Wang Junjie and Xicheng Wei

The purpose of this study was to comparatively investigate interfacial intermetallic compounds (IMCs) in the Sn3.0Ag0.5Cu3.0Bi0.05Cr/Cu (SACBC/Cu) and Sn3.0Ag0.5Cu/Cu…

Abstract

Purpose

The purpose of this study was to comparatively investigate interfacial intermetallic compounds (IMCs) in the Sn3.0Ag0.5Cu3.0Bi0.05Cr/Cu (SACBC/Cu) and Sn3.0Ag0.5Cu/Cu (SAC/Cu) solder joints, and to determine any differences.

Design/methodology/approach

The samples were annealed after isothermal ageing at 150°C for 0, 168 and 500 hours, and their cross-sections were observed by scanning electron microscopy and energy dispersive spectroscopy.

Findings

The interfacial IMC morphology in two joints had significant differences. For the Cu/SAC/Cu joints, the granular and short rod-like Ag3Sn particles attached on the surface and boundary of interfacial Cu6Sn5 grains were detected, and they coarsened observably with ageing time at 150°C, and lastly embedded at the grain boundaries. However, for the Cu/SACBC/Cu joints, there were tiny filamentous Ag3Sn growing on the surface of interfacial Cu6Sn5 grains, and the Ag3Sn had a tendency to break into nanoparticles, which would be distributed evenly and cover the IMC layer, profiting from the Bi and Cr precipitates from solder matrix during ageing.

Originality/value

The paper implies that the addition of Bi and Cr could affect the IMCs of joints, thereby delaying interfacial reactions between Sn and Cu atoms and improving the service reliability. The SACBC solder is a potential alloy for electronic packaging production.

Details

Soldering & Surface Mount Technology, vol. 26 no. 4
Type: Research Article
ISSN: 0954-0911

Keywords

1 – 10 of 143