Hiroshi Katanoda

Warm spraying—a novel coating process based on high-velocity impact of solid particles

Abstract In recent years, coating processes based on the impact of high-velocity solid particles such as cold spraying and aerosol deposition have been developed and attracting much industrial attention. A novel coating process called ‘warm spraying’ has been developed, in which coatings are formed by the high-velocity impact of solid powder particles heated to appropriate temperatures below the melting point of the powder material. The advantages of such process are as follows: (1) the critical velocity needed to form a coating can be significantly lowered by heating, (2) the degradation of feedstock powder such as oxidation can be significantly controlled compared with conventional thermal spraying where powder is molten, and (3) various coating structures can be realized from porous to dense ones by controlling the temperature and velocity of the particles. The principles and characteristics of this new process are discussed in light of other existing spray processes such as high-velocity oxy-fuel spraying and cold spraying. The gas dynamics of particle heating and acceleration by the spraying apparatus as well as the high-velocity impact phenomena of powder particles are discussed in detail. Several examples of depositing heat sensitive materials such as titanium, metallic glass, WC–Co cermet and polymers are described with potential industrial applications.

Effects of Spray Parameters and Heat Treatment on the Microstructure and Mechanical Properties of Titanium Coatings Formed by Warm Spraying

The microstructure and mechanical properties of Ti coatings deposited by warm spraying were investigated with the aim to find a set of optimum parameters for the spray process as well as for the subsequent heat treatment. Titanium powder was deposited with different nitrogen flow rates in a range from 0.5 to 1.5xa0m3/min. It was shown that spray parameters, which affect the temperature and velocity of in-flight particles, have significant influence on the fabricated coatings properties. Especially the increase of the warm spraying combustion pressure from 1 to 4xa0MPa resulted in an increase in the particle velocity to above 1100xa0m/s. This modification significantly increased the density and was beneficial for controlling the oxygen level in Ti coatings. Miniature tensile specimens with a total length of 9xa0mm were used to perform tensile tests for the Ti deposits. The optimal mechanical properties were achieved for specimens formed at a middle range of nitrogen flow rate (0.75xa0m3/min). Subsequently, several heat treatments were performed in order to enhance the mechanical properties of the as-sprayed coatings. It was found that the post-spray heat treatment significantly enhanced the strength and elongation of the Ti deposits determined by miniature specimen tensile test.

Effect of Reynolds Number on Pitot-Pressure Distributions in Underexpanded Supersonic Freejets

Conclusion In the present work a solution-adaptivesolver is presented to investigate the supersonicx8f ow over a backward-facingstep on mixed quadrilateral-triangular mesh. This solver incorporates the locally implicit scheme, two-level rex8e nement procedure,and a modix8e ed error indicator. In a Cartesian coordinate system the Euler equations are solved. Based on the comparison of adaptive meshes obtained using four differenterror indicators,themodix8e ed error indicatorcan incorporatethe advantagesand avoid the disadvantagesof the other three error indicators,which are 1⁄2 , M , and ! . According to the adaptivemesh obtainedusing the modix8e ed error indicator, the structure of backstep corner vortex, expansion wave, and oblique shock wave is distinctly captured.

Effects of Spray Parameters and Post-spray Heat Treatment on Microstructure and Mechanical Properties of Warm-Sprayed Ti-6Al-4V Coatings

Warm spray is a novel thermal spray technique that allows the formation of dense and relatively pure Ti-6Al-4V coatings due to its capability to control the temperature of the propellant gas by diluting the combustion flame with an inert gas such as nitrogen. Recently, its combustion pressure has been increased from 1 to 4xa0MPa aiming to further increase particle velocity to over 1000xa0m/s. Two series of coatings with combustion pressure of 1 and 4xa0MPa and various nitrogen flow rates were prepared in this study. Effects of combustion pressure and nitrogen flow rate on the microstructure and mechanical properties of the Ti-6Al-4V coatings were systematically studied. Miniature tensile specimens with a total length of about 9xa0mm were used for static tensile tests. It was found that the spray parameters affect both the porosity and oxygen content of the coatings significantly and had remarkable effects on their mechanical properties. High level of porosity in the Ti-6Al-4V coatings reduced the effective cross-sectional area of the mini-specimens and caused a drop in their tensile strength and Young’s modulus. Subsequent heat treatments were found effective in significantly recovering the mechanical properties of the as-sprayed coatings.

Warm Spraying of High-Strength Ni-Al-Bronze: Cavitation Characteristics and Property Prediction

Bronze materials such as Ni-Al-bronze show exceptional performances against cavitation erosion, due to their high fatigue strength and high strength. These materials are used for ship propellers, pump systems or for applications with alternating stresses. Usually, the respective parts are cast. With the aim to use resources more efficiently and to reduce costs, this study aimed to evaluate opportunities to apply bronze as a coating to critical areas of respective parts. The coatings should have least amounts of pores and non-bonded areas and any contaminations that might act as crack nuclei and contribute to material damages. Processes with low oxidation and high kinetic impacts fulfill these criteria. Especially warm spraying, a nitrogen-cooled HVOF process, with similar impact velocities as cold gas spraying but enhanced process temperature, allows for depositing high-strength Ni-Al-bronze. This study systematically simulates and evaluates the formation and performance of warm-sprayed Ni-Al-bronze coatings for different combustion pressures and nitrogen flow rates. Substrate preheating was used to improve coating adhesion for lower spray parameter sets. Furthermore, this study introduces an energy-based concept to compare spray parameter sets and to predict coating properties. Coatings with low porosities and high mechanical strengths are obtained, allowing for a cavitation resistance similar to bulk material.

Studv on Flow Characteristics oi Compouna Swirl Jet (Effect of Nozzle Depth)

湯 之 谷 祥 平 ッ 鹿 児 島 大 院 ) , 福 原 稔 ( 鹿 児 島 大 ) 片 野 田 洋 ( 鹿 児 島 大 ) , 危 田 昭 雄 ( 鹿 児 島 大 ) Studv on Flow Characteristics oi Compouna Swirl Jet (Effect of Nozzle Depth) Syohei YUNOTANI, Minoru FUKUHARA Hiroshi KATANODA and Akio K A M E D A A B S T R A C T A c o m p o u n d s w i r l j e t w h i c h cons i s t s of a n a n n u l a r s w i r l i n g j e t a n d a c o a x i a l f r ee j e t i s e f f e c t i v e as a p u s h flow o f t h e p u s h p u l l v e n t i l a t o r . I n t h i s p a p e r , to e n h a n c e t h e c o l l e c t i n g c a p a b i l i t y o f t h e j e t f l o w , t h e e x p e r i m e n t w a s c a r r i e d o u t u n d e r t h e c o n d i t i o n o f l o c a t i n g t h e i n n e r t u b e o f f r ee j e t to t h e u p s t r e a m . T h e c o l l e c t e d flow r a t e o f t h e j e t flow w a s c a l c u l a t e d f o r v a r i o u s flow r a t e o f t h e s w i r l i n g j e t a n d nozz le d e p t h b y t h e m e a s u r e m e n t o f v e l o c i t y d i s t r i b u t i o n . A s a r e s u l t , i t w a s f o u n d t h a t t h e o p t i m u m c o l l e c t e d f l o w r a t e is o b t a i n e d w i t h o u t t h e s w i r l i n g f l o w , w h e n t h e nozz le d e p t h i n c r e a s e s . T h e g e n e r a t i o n m e c h a n i s m w a s c l a r i f i e d b y t h e flow v i s u a l i z a t i o n n e a r n o z z l e e x i t u s i n g P I V . T h e f l o w d e v e l o p i n g p r o c e s s o f t h e j e t f l o w w a s c o n f i r m e d b y s h o w i n g t h e c o l l e c t e d f l o w r a t e . K e y W o r d : F r e e j e t , S w i r l i n g f l o w , P u s h P u l l v e n t i l a t o r , P a r t i c l e i m a g e v e l o c i m e t r y

Effect of Depth of Discnarging Plates for Sediment Removal on Hydraulic Conveying Characteristics

A B S T R A C T I n t h e h y d r a u l i c c o n v e y i n g o f s o l i d l i q u i d f l o w i n t h e c o n d u i t , t h e d i s c h a r g i n g p l a t e s w e r e p r o p o s e d by t h e a u t h o r s to t r a n s p o r t t h e p a r t i c l e s t h a t h a d p i l e d u p . I n t h i s pape i ., t h e d e p t h o f t h e p l a t e s i n s t a l l e d f o r t h e p a r t i c l e beds w a s c h a n g e d a n d t h e f l o w o f t h e p a r t i c l e s w a s e x a m i n e d b y t h e f l o w v i s u a l i z a t i o n . A s a r e s u l t , i t w a s f o u n d t h e o p t i m u m d e p t h o f t h e p l a t e s f o r t h e p a r t i c l e beds ex i s t s . I t w a s c o n f i r m e d t h a t t h e e f fec ts o f i n t e r v a l a n d o v e r a l l l e n g t h o f t h e p l a t e s i n t h i s o p t i m u m c o n d i t i o n a re q u a l i t a t i v e l y s i m i l a r w i t h t h e case t h a t t h e d e p t h o f t h e p l a t e f o r t h e p a r t i c l e beds is s h a l l o w as t h e p r e v i o u s r e p o r t . K e y w o r d s : H y d r a u l i c c o n v e y i n g . S o l i d l i q u i d f l ow, Scour , S l u r r y

Effect of Pipe-Diameter Ratio on Heat Transfer and Flow Characteristics of Impinging Jet from Coaxial Circular Pipe

The impinging jet is widely used in the industrial field, as high heat transfer characteristics are obtained in the vicinity of a stagnation point on the object surface. In this paper, the heat transfer characteristics on the impinging wall after being blown off through a coaxial circular pipe were examined by changing the pipe-diameter ratio and the velocity ratio. As a result, the optimum values of the pipe-diameter ratio and the velocity ratio were found in the given conditions. The influence of the pipe-diameter ratio and the velocity ratio on the flow structure was clarified by the flow visualization.

Visualization of Supersonic Jet from High-Velocity Oxy-Fuel Thermal Spraying Gun by Numerical Simulation

Supersonic jets from a high-velocity oxy-fuel thermal spraying gun have been simulated and visualized by numerical analysis. The thermal spraying gun in the present simulation has the same shape as that of a commercially used gun. To visualize the jet structure, the equi-Mach number contours of supersonic jets have been depicted, and the Mach number and static pressure distributions along the jet axis have been, calculated both for under-expanded and correctly-expanded supersonic jets. For under-expanded jets, the diamond shock pattern has been observed.

Study on Particle Transport Characteristics of Doublet Type Suction Nozzle

In the pneumatic transportation, it was proposed by the authors that the effective and stable feeding of the particles can be attained by mounting the injection flow at the center of the suction nozzle. In this paper, we examined the influence of pipe diameter ratio on the nozzle performance. As a result, it was found that the optimum pipe diameter ratio exists. The various particles movement from different pipe diameter ratio was clarified by the flow visualization nearthe suction nozzle.