A series of Fe-based amorphous composite coatings, mixed with ceramic particles, are prepared by flame spraying water atomized powder The morphology, structure and mechanical properties are investigated by scanning electron microscopy, X-ray diffraction and micro- and nano-indenter, respectively The residual stress and influence of process parameters on residual stress, such as ceramic content, type and spraying distance, have been systematically studied The results reveal that the coating with 30 wt% Al2O3 has shown excellent properties, such as porosity of 05% and micro-hardness of 7947 HV Furthermore, the results reveal that the residual stress decreased with the addition of ceramic particles, up to a threshold value, followed by a linear increase The maximum value of 141 MPa has been achieved for FeBSiNb coating, with the Al2O3 content of 20% However, the high melting point of feedstock powder and high thermal conductivity of impacting ceramic particles reduce the impacting effect because of the increased enthalpy of the coating and decreased kinetic energy of the impacting ceramic particles In addition, spraying distance can also influence the residual stress of coatings Once the spray distance was increased from 150 mm to 250 mm, the residual tensile stress of the coating decreased from 208 MPa to −115 MPa, where negative sign signifies that the residual stress has become compressive stress

Influence of ceramic particles and process parameters on residual stress of flame-sprayed Fe-based coatings

Shot peening was used synchronously to improve Fe-based amorphous coating performance by delivering ZrO2 ceramic particles into a low-temperature region of a flame during the high velocity oxygen flame (HVOF) spray process. The coating became denser, and its hardness became higher via the new process. Moreover, the compressive residual stress was induced by shot peening. The results from the dry friction test indicated that the coating’s wear resistance was enhanced obviously. The wear mechanism of coatings with and without shot peening is an abrasive wear combined with an oxidation wear at wear test conditions of a low load and a low frequency. The coating with the best wear resistance did not have the strongest microhardness but had the highest compressive residual stress. The compressive residual stress had a significant positive influence on the wear resistance at a low frequency, while its effect is weakened at a high frequency.

Synchronous Shot Peening Applied on HVOF for Improvement on Wear Resistance of Fe-based Amorphous Coating

Shot peening was induced by utilizing the particles that flow out of the nozzle in a WPPA-HVOF process. For investigation of the peening particles, a model was built to simulate the HVOF spraying process including the temperature, velocity, pressure field of the flame, and the reaction of kerosene oxidation. The effect of incident velocity, incident position, and the diameter on the in-flight particle was presented. Incident velocity is an important factor for the synchronization of shot peening and coating deposition. The critical velocity was introduced to describe the particle state after hitting onto the substrate. The velocity and temperature of small particles injected in the barrel were measured experimentally to verify the model reliability. Experimental results reveal that the particle injected in the barrel deposited onto the substrate and the particle injected out of the nozzle rebounded, which agrees well with the predicted result.

Numerical Investigation of Particles in Warm-Particle Peening-Assisted High-Velocity Oxygen Fuel (WPPA-HVOF) Spraying

The contribution aims to give a perspective of the ever-expanding range and variety of methods of manufacturing rapidly-solidified (RS) particulates and the fundamental characteristics of their products. Particular attention will be given to more recent developments and to possible criteria for assessing their efficacy. These might include rating of the following capabilities: 

(i)

to generate a required particle size or size distribution and particle morphology.




(ii)

to achieve a required structural state within the particulate.




(iii)

to successfully process materials of different characteristics such as fusibility and reactivity.




(iv)

to accommodate minimum levels of production volume and rate.






Criteria (i) and (ii) are closely linked and rather basic and will receive particular attention in the contribution. It is concluded that understanding of the mechanisms by which the various methods form and solidify the particulate is still largely in its infancy and that relationships between operating variables and RS structure remain to be determined for many of these production processes. In view of uncertainties concerning applicable cooling and solidification conditions for particular processes, there is some merit in ranking them in terms of their ability to produce a given microstructure or constitution at a particular particle size. Evaluation of properties as a function of RS microstructure or constitution and of variables in any subsequent consolidation remain fruitful areas of further study.

Production and Characterization of Rapidly-Solidified Particulates

With the development of automotive and toy industries, more and more plastics injection dies and moulds are required. Many researchers attempt to find new processes, which can reduce manufacturing costs and delivery time and obtain dimensional accuracy and high quality sur faces for dies and moulds. This thesis describes the development of a novel hybrid process for the manufacture of plastics injection moulds. Compared with conventional procedures, the hybrid process can produce high quality plastics injection moulds at low cost and with short lead times. The hybrid process consists of two stages electrofor ming and simultaneous spray peening. This work undertakes research and development of electroforming aspects of the hybrid process. All techniques and theories will be discussed in this thesis. The feasibility of using electroformed shells to make the working surface of plastics injection moulds was investigated. The important mechanical properties of a nickel shell, such as hardness, tensile strength, ductility and internal stress, were researched and improved by using various operating conditions and adding some agents. The pulse plating power supply was designed to improve the mechanical properties of the nickel shell. The influence of pulse plating parameters on electroforming shell accuracy was analysed. Mandrel materials were also investigated. The accuracy of reproduction by electroforming was measured and analysed. The interface between the nickel shell and spray metal was analysed by scanning electron-microscope and the bond strength measured using a direct tensile testing method. Finally, two injection moulds were made up and tested under two conditions, plastics injection and high pressure casting of aluminium. The results show that the moulds made by the hybrid process can be used successfully to produce plastics components, but can not be used for high pressure of casting aluminium. This application of the hybrid process has shown promise in the automotive and toy industries.

Electroforming procedures for shells of moulds and dies for subsequent simultaneous spray peening

A new process, simultaneous spray peening (SSP), is described which comprises the spray deposition of metals together with simultaneous shot peening. This combined incremental operation allows either thick or thin deposits to be made in ferrous or non-ferrous metals. The deposits are hot worked and densified during the process so improving their properties compared with more conventional spray deposits. An additional advantage is that the inherent residual tensile stresses of spray deposition are counter-balanced by the compressive stresses caused by peening. By control of the simultaneous peening operation it is shown that the residual stresses in SSP deposits can be maintained at any required positive or negative level. Examples and structures are shown of SSP products made from gas-atomized melts, by arc spray, and by plasma spray.

A. R. E. Singer

Papers

Simultaneous spray deposition and peening of metals (SSP)