JP2017193763A - Gas atomized titanium powder - Google Patents
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本発明は、ガスアトマイズ法により製造されたガスアトマイズチタン粉末に関し、更に詳しくは、粉末冶金法による成形加工に適した微細で流動性に優れたガスアトマイズチタン粉末に関する。なお、本明細書ではチタンは特にことわりのない限りＴｉ又はＴｉ合金を意味する。 The present invention relates to a gas atomized titanium powder produced by a gas atomizing method, and more particularly to a fine gas atomized titanium powder suitable for molding by a powder metallurgy method and having excellent fluidity. In the present specification, titanium means Ti or a Ti alloy unless otherwise specified.
チタンは、比強度が大きくて耐食性に優れるので、生体適合性等に高い性能を示すが、一方で機械加工性や塑性加工性に劣ることから、加工コストが高いという欠点がある。この欠点を克服するため、３次元複雑形状の金属部品をニアネットシェイプで作製できて後加工を殆ど必要としない粉末冶金法が、チタンの有効な加工法として期待されており、これに伴って粉末冶金用原料としてのチタン粉末の需要が増えている。 Titanium has high specific strength and excellent corrosion resistance, and thus exhibits high performance in biocompatibility and the like, but has a disadvantage of high processing cost because it is inferior in machinability and plastic workability. In order to overcome this drawback, a powder metallurgy method that can produce a metal part having a three-dimensional complicated shape with a near net shape and requires little post-processing is expected as an effective processing method of titanium. There is an increasing demand for titanium powder as a raw material for powder metallurgy.
粉末冶金法に使用されるチタン粉末には、微細粒であること、及び流動性のよいことが求められる。微細粒であることは成形品の緻密度の点から重要であり、流動性のよいことは成形品の均質性の点から重要である。これらの要望を満たすために、粉末冶金用チタン粉末としては、ガスアトマイズ法により製造されたチタン粉末が好適とされている（特許文献１）。 Titanium powder used for powder metallurgy is required to be fine and have good fluidity. The fine particles are important from the viewpoint of the density of the molded product, and the good fluidity is important from the point of homogeneity of the molded product. In order to satisfy these demands, titanium powder produced by a gas atomizing method is suitable as titanium powder for powder metallurgy (Patent Document 1).
ガスアトマイズ法によると、表面が滑らかな微細粒子からなるチタン粉末が製造される。しかし、その粉末の流動性は粒子の形状、性状から期待されるほどには良好とは言えず、実用レベルに達していない。なぜなら、ガスアトマイズ法で製造されたチタン粉末では、個々の粒子の真球度は比較的高いが、その粒子に更に微細な粒子がコブのように付着するため、結果として粒子の真球度が低下する。微細粒子にコブのように付着する非常に微細な粒子はサテライトと呼ばれており、チタン粉末粒子の真球度を低下させて、その粒子の流動性を阻害する原因となっている。このため、サテライトを軽減する方向で製法に様々な工夫が講じられているが、効果が小さい上にコストが嵩む問題がある。 According to the gas atomization method, titanium powder made of fine particles having a smooth surface is produced. However, the fluidity of the powder is not as good as expected from the shape and properties of the particles, and has not reached the practical level. This is because the sphericity of each particle is relatively high in the titanium powder produced by the gas atomization method, but finer particles adhere to the particle like a bump, resulting in a decrease in the sphericity of the particle. To do. Very fine particles adhering to the fine particles like bumps are called satellites, which lowers the sphericity of the titanium powder particles and inhibits the fluidity of the particles. For this reason, various ideas have been devised in the manufacturing method in the direction of reducing the satellite, but there is a problem that the effect is small and the cost is increased.
加えて、時代の要請から３Ｄプリンタによる複雑形状で緻密な成形品が求められ始め、これに伴って今までよりも更に微細なチタン粉末が求められるようなったが、一般に粉末の粒子径と流動性との間には相関関係が成立し、チタン粉末でも例外ではない。このため、チタン粉末は微細粒ほど流動性が低下し、粒子径が４５μｍ以下になると、その流動性は実用レベルから相当に逸脱したものになる。微細粒ほど流動性が悪化するのは、粉末粒子の全表面積が大きくなることが理由である。 In addition, due to the demands of the times, there has been a demand for dense and complex molded products by 3D printers, and as a result, finer titanium powders have been required than before, but generally the particle size and flow of the powder There is a correlation between the properties and titanium powder is no exception. For this reason, the fluidity of titanium powder decreases as the particles become finer, and when the particle diameter becomes 45 μm or less, the fluidity deviates considerably from the practical level. The reason why the fluidity deteriorates as the particles become finer is that the total surface area of the powder particles increases.
このようなことから、粉末冶金用チタン粉末の分野では、粒子径が４５μｍ以下の微細粉末でありがら、なおかつ流動性が実用レベルに達するものが求められている。ちなみに、実用レベルの流動性とは、ＪＩＳＺ２５０２：２０１２に規定された金属粉−流動度測定方法を用いて表すと、漏斗に入れた粉末が、漏斗を叩いて流れを誘導することなく、オリフィスから自然に流れ出すことができ、５０ｇの粉末が規定のオリフィスから全量流出するのに要する時間を数値化できる程度のものである。 For this reason, in the field of titanium powder for powder metallurgy, there is a demand for a fine powder having a particle size of 45 μm or less and having fluidity reaching a practical level. By the way, the fluidity at the practical level is expressed using the metal powder-fluidity measurement method defined in JISZ2502: 2012, and the powder placed in the funnel can be passed from the orifice without inducing the flow by hitting the funnel. It can flow out naturally, and the amount of time required for 50 g of powder to flow out from the specified orifice can be quantified.
本発明の目的は、ガスアトマイズ法によるチタン微細粒からなり、しかも流動性に優れたガスアトマイズチタン粉末を提供することにある。 An object of the present invention is to provide a gas atomized titanium powder composed of fine titanium particles by a gas atomizing method and having excellent fluidity.
上記目的を達成するために、本発明者はガスアトマイズ法により製造されたチタン微細粉末粒子へのサテライトの付着を不可避と考え、そのサテライトの軽減に代わる新たな流動性改善策について検討した。その結果、以下の事実が判明した。 In order to achieve the above object, the present inventor considered that adhesion of satellites to titanium fine powder particles produced by the gas atomization method is unavoidable, and studied a new fluidity improvement measure to replace the reduction of the satellites. As a result, the following facts were found.
微細粉末粒子の流動性に影響を与える因子は多岐にわたり、且つ相互に影響しあう。代表的な因子としては、粒子径及び粒子形状（真球度）がある。しかし、それ以外にも例えば粒子表面の平滑度がある。ガスアトマイズ法により製造されたチタン微細粉末粒子の場合は、製法上の特性として粒子表面の平滑度が非常に高くなり、その特性自体は流動性上はむしろ望ましいとの考えから、専ら平滑度以外の、粒子形状（真球度）の面から、流動性が追求されてきた。これが前述したサテライトの低減である。 Factors affecting the fluidity of fine powder particles are diverse and affect each other. Typical factors include particle diameter and particle shape (sphericity). However, other than that, for example, there is smoothness of the particle surface. In the case of titanium fine powder particles manufactured by the gas atomization method, the smoothness of the particle surface is very high as a characteristic in the manufacturing method, and the characteristic itself is rather desirable in terms of fluidity, and therefore, other than smoothness. From the aspect of particle shape (sphericity), fluidity has been pursued. This is the satellite reduction described above.
チタン粉末粒子の真球度は、円形度にて定量的に評価可能である。円形度とは粒子形状の丸さの度合いを表し、これが１に近いほど粒子形状は真球となる。円形度が０．８以上の粒子は球状とみなすことができるので、円形度が０．８未満の非球状粒子の個数割合が少ないほど流動性が向上することになる。ガスアトマイズ法によるチタン粉末では、主にサテライトの影響のために、円形度が０．８未満である非球状粒子の個数割合は意外に多く、７０％を超える。すなわち、円形度が０．８以上である球状粒子は、全体の３０％以下と少ないのが普通である。このため、サテライトの低減による非球状粒子個数割合の低減が、チタン粉末の流動性の改善に有効とされる。 The sphericity of the titanium powder particles can be quantitatively evaluated by the circularity. The degree of circularity represents the degree of roundness of the particle shape, and the closer this is to 1, the more the particle shape becomes a true sphere. Since particles having a circularity of 0.8 or more can be regarded as spherical, the smaller the proportion of non-spherical particles having a circularity of less than 0.8, the better the fluidity. In the titanium powder produced by the gas atomization method, the ratio of the number of non-spherical particles having a circularity of less than 0.8 is surprisingly high, exceeding 70%, mainly due to the influence of satellites. That is, the number of spherical particles having a circularity of 0.8 or more is usually as small as 30% or less. For this reason, the reduction of the number ratio of the non-spherical particles due to the reduction of the satellite is effective in improving the fluidity of the titanium powder.
しかしながら、前述したとおり、サテライトの低減は技術的に難しく、十分な成果を挙げるに至っていないのが実情である。そこで本発明者は、複雑に影響しあう多くの流動性因子のなかから特に粒子表面の平滑度に着目し、これと流動性との関係を子細に調査した。その結果、これまではガスアトマイズ法の長所とされていた粒子表面の平滑さを逆に悪化させるのが、ガスアトマイズ法によるチタン微細粉末粒子では効果的なことが判明した。 However, as described above, it is technically difficult to reduce satellites, and in fact, sufficient results have not been achieved. Therefore, the present inventor paid particular attention to the smoothness of the particle surface from among many fluidity factors that affect each other in a complicated manner, and investigated the relationship between this and the fluidity in detail. As a result, it has been found that the fine particles of titanium by the gas atomization method are effective in deteriorating the smoothness of the particle surface, which has been an advantage of the gas atomization method.
すなわち、流動性への影響としては、粒子径が４５μｍ以下というような微細粒レベルでは、粒子表面の滑らかさより粗さが有効となり、特に、粒子表面の最大高さ粗さの影響度が大きく、これを２５ｎｍ以上と大きくすることにより、円形度が０．８未満の非球状粒子の個数割合が７０％を超えたままでも、その粉末の流動性が著しく改善されることが判明したのである。 That is, as an influence on fluidity, at a fine particle level such as a particle diameter of 45 μm or less, the roughness is more effective than the smoothness of the particle surface, in particular, the influence of the maximum height roughness of the particle surface is large, It has been found that by increasing this to 25 nm or more, the fluidity of the powder is remarkably improved even when the number ratio of the non-spherical particles having a circularity of less than 0.8 exceeds 70%.
ちなみに、ガスアトマイズ法で通常に製造されるチタン粉末の表面は、最大高さ粗さで表すと、１０ｎｍ程度と非常に平滑である。この平滑さを２５ｎｍ以上に悪化させるには、例えば低濃度の水溶性チタン化合物を含有した水溶液による湿式表面酸化等の化学的手法があり、湿式表面酸化の場合、酸化度により粒子表面の最大高さ粗さを広範囲に調整することができる。 Incidentally, the surface of the titanium powder normally produced by the gas atomization method is very smooth, about 10 nm, when expressed by the maximum height roughness. In order to deteriorate the smoothness to 25 nm or more, for example, there is a chemical method such as wet surface oxidation with an aqueous solution containing a low-concentration water-soluble titanium compound, and in the case of wet surface oxidation, the maximum height of the particle surface depends on the degree of oxidation. The roughness can be adjusted over a wide range.
本発明のガスアトマイズチタン粉末はかかる知見を基礎とし開発されたものあり、ガスアトマイズ法により製造されたチタン微細粒からなり、その粒子表面の最大高さ粗さが２５ｎｍ以上２００ｎｍ以下であることを構成上の特徴点とする。 The gas atomized titanium powder of the present invention has been developed on the basis of such knowledge, and is composed of fine titanium particles produced by the gas atomization method, and the maximum height roughness of the particle surface is 25 nm or more and 200 nm or less. The feature point.
本発明のガスアトマイズチタン粉末においては、粒子表面の最大高さ粗さが２５ｎｍ以上と従来より大きくなる（粗くなる）ことにより、粒子形状（真球度）を改善せずとも、粉末粒子の流動性が改善される。粉末粒子の流動性に影響する因子は多く、しかも、それが複雑に関係しているので、本発明で流動性が改善される理由は定かではないが、粒子表面の最大高さ粗さが大きくなる（粗くなる）と、粉末粒子全体の表面積は増える傾向となるものの、粉末粒子間の密着性は低下し、密着性の低下による好影響が、表面積の増大による悪影響を凌ぐことが考えられる。事実、粒子表面の最大高さ粗さが２００ｎｍを超えると、逆に流動性が悪化する傾向が見られる。 In the gas atomized titanium powder of the present invention, the maximum height roughness of the particle surface is 25 nm or more and becomes larger (rougher) than before, so that the fluidity of the powder particles is improved without improving the particle shape (sphericity). Is improved. There are many factors that affect the fluidity of powder particles, and because they are complicatedly related, the reason why the fluidity is improved in the present invention is not clear, but the maximum height roughness of the particle surface is large. When it becomes (rough), the surface area of the entire powder particles tends to increase, but the adhesion between the powder particles decreases, and it is considered that the positive effect due to the decrease in adhesion surpasses the adverse effect due to the increase in surface area. In fact, when the maximum height roughness of the particle surface exceeds 200 nm, the fluidity tends to deteriorate.
すなわち、この最大高さ粗さが２５ｎｍ未満では、流動性の改善に目立った効果が得られない。反対に、２００ｎｍを超えると、流動性の悪化を招く。特に好ましい最大高さ粗さは、２５ｎｍ以上１００ｎｍ以下である。 That is, when the maximum height roughness is less than 25 nm, a remarkable effect for improving the fluidity cannot be obtained. On the contrary, when it exceeds 200 nm, fluidity is deteriorated. A particularly preferred maximum height roughness is 25 nm or more and 100 nm or less.
本発明のガスアトマイズチタン粉末は、粒子径が１０μｍオーダーの微細粒の分野で特に有効である。具体的には、その粒子径はＤ90で１５０μｍ以下３５μｍ以上が好ましい。粒子径がＤ90で１５０μｍを超えると、そもそも流動性の悪化が問題になり難い。反対に、粒子径がＤ90で３５μｍ未満になると、粒子表面の最大高さ粗さを粗くしても、流動性の改善に目立った効果は得られない。特に好ましい粒子径はＤ90で１００以下３５μｍ以上である。 The gas atomized titanium powder of the present invention is particularly effective in the field of fine particles having a particle size of the order of 10 μm. Specifically, the particle diameter is preferably 150μm or less 35μm or more D 90. When the particle diameter exceeds 150 μm at D 90 , the deterioration of fluidity is unlikely to be a problem in the first place. On the other hand, when the particle diameter is less than 35 μm at D 90 , even if the maximum height roughness of the particle surface is roughened, a remarkable effect for improving the fluidity cannot be obtained. Particularly preferred particle diameter is 100 or less 35μm or more D 90.
粒子形状（真球度）については、その真球度が低い非球状粒子の割合が少ないほど流動性は改善され好ましいが、現実にはその割合を小さくすることは難しい。本発明のガスアトマイズチタン粒子は、その割合を格別小さくせずとも粉末粒子の流動性を改善できる点に特徴があり、具体的には円形度が０．８未満の非球状粒子の個数割合が７０％以上でも十分に有効である。とはいえ、この個数割合が大きくなると流動性に支障が生じ始める。この観点から、この個数割合は９０％以下が望ましく８０％以下が特に望ましい。 As for the particle shape (sphericity), the smaller the proportion of non-spherical particles having a lower sphericity, the better the fluidity, but in reality it is difficult to reduce the proportion. The gas atomized titanium particles of the present invention are characterized in that the fluidity of powder particles can be improved without particularly reducing the proportion thereof. Specifically, the number proportion of non-spherical particles having a circularity of less than 0.8 is 70. % Or more is sufficiently effective. Nonetheless, when this number ratio increases, problems with fluidity begin to occur. From this viewpoint, the number ratio is desirably 90% or less, and particularly desirably 80% or less.
本発明のガスアトマイズチタン粉末は、ガスアトマイズ法による微細粒からなるにもかかわらず、粒子表面の最大高さ粗さを２５ｎｍ以上２００ｎｍ以下としたことにより、流動性に優れるので、粉末冶金用原料に使用して粉末冶金製品の品質を高めるのに有効である。 The gas atomized titanium powder of the present invention is used as a raw material for powder metallurgy because it is excellent in fluidity because the maximum height roughness of the particle surface is 25 nm or more and 200 nm or less despite being made of fine particles by the gas atomization method. It is effective to improve the quality of powder metallurgy products.
以下に本発明の実施形態を説明する。 Embodiments of the present invention will be described below.
本実施形態では、第１工程として、Ｔｉ又はＴｉ合金の微細粒からなるチタン粉末を、不活性ガスを用いたガスアトマイズ法により製造する。 In the present embodiment, as the first step, titanium powder made of fine particles of Ti or Ti alloy is manufactured by a gas atomizing method using an inert gas.
第２工程として、製造されたチタン粉末を篩い分けにより分級し、粒子径が所望値に揃ったチタン粉末を得る。得られたチタン粉末の粒子表面は、最大高さ粗さで１０ｎｍ程度と非常に平滑である。粉末粒子の真球度は、前述した円形度が０．８未満である非球状粒子の個数割合で表して７０％以上と、良いとは言えない。 As a second step, the produced titanium powder is classified by sieving to obtain a titanium powder having a particle diameter of a desired value. The particle surface of the obtained titanium powder is very smooth with a maximum height roughness of about 10 nm. The sphericity of the powder particles cannot be said to be as good as 70% or more in terms of the number ratio of the non-spherical particles whose circularity is less than 0.8.
このようなチタン粉末の場合、粒子径が１５０μｍ以下であると流動性が良くなく、粉末冶金原料として適さない。そこで本実施形態では、第３工程として、チタン粉末の粒子表面を低濃度酸液による湿式表面酸化により酸化処理して、その表面粗さを粗くする。具体的には、最大高さ粗さを２５ｎｍ以上２００ｎｍ以下、望ましくは２５ｎｍ以上１００ｎｍ以下に調整する。この最大高さ粗さの調整は、酸液の濃度変更により可能である。 In the case of such a titanium powder, if the particle size is 150 μm or less, the fluidity is not good and it is not suitable as a powder metallurgy raw material. Therefore, in the present embodiment, as a third step, the particle surface of the titanium powder is oxidized by wet surface oxidation with a low-concentration acid solution to roughen the surface roughness. Specifically, the maximum height roughness is adjusted to 25 nm to 200 nm, preferably 25 nm to 100 nm. The maximum height roughness can be adjusted by changing the concentration of the acid solution.
粒子表面の粗さ調整を受けたチタン粉末は、粒子径が１５０μｍ以下と微細で、しかも真球度が円形度０．８未満の非球状粒子の個数割合で７０％以上と低く、流動性の観点からは本来的に不利な形状、性状であるにもかかわらず、流動性に優れ、粉末冶金原料としても実用レベルの高い流動性を示す。 Titanium powder having undergone grain surface roughness adjustment is fine with a particle diameter of 150 μm or less, and the number ratio of non-spherical particles having a sphericity of less than 0.8 circularity is as low as 70% or more. Despite its inherently disadvantageous shape and properties, it is excellent in fluidity and exhibits high fluidity at a practical level as a powder metallurgy raw material.
第３工程で使用する液は、水溶性チタン化合物を含有した溶液で、具体的にはペルオキソチタン水溶液、四塩化チタン水溶液、硫酸チタン水溶液などがあり、なかでもペルオキソチタン水溶液はｐＨが中性付近なため、取扱いの点から好ましい。水溶性チタン化合物を含有した溶液処理以外では、フッ硝酸等のチタンをエッチングする溶液で処理するなどが粒子表面の最大高さ粗さを大きくするのに有効であるが、エッチング速度制御が難しいため、粒子表面の最大高さ粗さの調整が難しい。 The liquid used in the third step is a solution containing a water-soluble titanium compound, and specifically includes a peroxotitanium aqueous solution, a titanium tetrachloride aqueous solution, a titanium sulfate aqueous solution, etc. Among them, the peroxotitanium aqueous solution has a pH near neutral. Therefore, it is preferable from the viewpoint of handling. Other than solution treatments containing water-soluble titanium compounds, treatment with a solution that etches titanium, such as fluorinated nitric acid, is effective in increasing the maximum height roughness of the particle surface, but it is difficult to control the etching rate. It is difficult to adjust the maximum height roughness of the particle surface.
チタン粉末として、特許文献１に記載の不活性ガスによるガスアトマイズ法により作製したＴｉ−６Ａｌ−４ＶからなるＴｉ合金粉末を用意し、これを篩分けして、４５μｍアンダー品と４５〜１０６μｍ品の２種類を得た。４５μｍアンダー品の粒子径はＤ90で３５μｍ、４５〜１０６μｍ品の粒子径はＤ90で１００μｍである。 As the titanium powder, Ti alloy powder made of Ti-6Al-4V prepared by the gas atomization method using an inert gas described in Patent Document 1 is prepared, and this is sieved to obtain a 45 μm under product and a 45 to 106 μm product 2 Got a kind. The particle size of the 45 μm under product is 35 μm at D 90 and the particle size of the product of 45 to 106 μm is 100 μm at D 90 .
チタン粉末の真球度を前述した円形度が０．８未満の非球状粒子の個数割合（％）にて評価したところ、前者の３５μｍ品における非球状粒子の個数割合は７２．４％、後者の１００μｍ品における非球状粒子の個数割合は７９．８％であり、サテライトのために共に７０％を超えた。円形度が０．８未満の非球状粒子の個数割合（％）は粉体画像解析装置（セイシン製ＰＩＴＡ−３）にて測定した。 When the sphericity of the titanium powder was evaluated by the number ratio (%) of nonspherical particles having a circularity of less than 0.8, the number ratio of nonspherical particles in the former 35 μm product was 72.4%, the latter. The number ratio of non-spherical particles in the 100 μm product was 79.8%, and both exceeded 70% for the satellite. The number ratio (%) of non-spherical particles having a circularity of less than 0.8 was measured with a powder image analyzer (PITA-3 manufactured by Seishin).
２種類のチタン粉末（３５μｍ品及び１００μｍ品）を希薄なペルオキソチタン水溶液に浸漬した後、その水溶液から回収し、１１０℃の大気下で乾燥することにより、各粉末粒子の表面を酸化した。ペルオキソチタン水溶液の濃度を様々に変更することにより、各粉末粒子の表面に様々な最大高さ粗さを付与した。酸化処理前の粒子表面の最大高さ粗さは各粉末とも１２μｍであり、ペルオキソチタン水溶液の濃度を高くすることにより、酸化が進行して最大高さ粗さが大きくなる。最大高さ粗さは、レーザー顕微鏡（キーエンス社製ＶＫ−Ｘ２５０／２６）にて測定した。 Two types of titanium powder (35 μm product and 100 μm product) were immersed in a dilute aqueous peroxotitanium solution, recovered from the aqueous solution, and dried in the atmosphere at 110 ° C. to oxidize the surface of each powder particle. By varying the concentration of the aqueous peroxotitanium solution, various maximum height roughnesses were imparted to the surface of each powder particle. The maximum height roughness of the particle surface before the oxidation treatment is 12 μm for each powder. By increasing the concentration of the peroxotitanium aqueous solution, the oxidation proceeds and the maximum height roughness increases. The maximum height roughness was measured with a laser microscope (VK-X250 / 26 manufactured by Keyence Corporation).
２種類のチタン粉末（３５μｍ品及び１００μｍ品）について各々得られた最大高さ粗さが異なる粉末の流動性をＪＩＳＺ２５０２：２０１２「金属粉−流動度測定方法」に規定された流動度（秒／５０ｇ）により測定評価した。測定された各粉末の流動性を、粉末仕様（粒子径、非球状粒子の個数割合、ペルオキソチタン水溶液濃度、最大高さ粗さ）と共に表１に示す。この流動度（秒／５０ｇ）は小さいほど流動性に優れ、流動度が４０秒／５０ｇ以下で流れるものを「◎（良好）」、流動するも流動度が４０秒／５０ｇ超えるものを「〇（可）」、流動しないものを「×（不可）」とし、ここでは粉末冶金法での成形加工性を考慮して「◎（良好）」のみを合格とした。 The fluidity of the powders having different maximum height roughness obtained for each of the two types of titanium powders (35 μm product and 100 μm product) was determined according to JISZ2502: 2012 “Metal powder—fluidity measurement method” (seconds / second). 50 g). The measured fluidity of each powder is shown in Table 1 together with powder specifications (particle diameter, number ratio of non-spherical particles, peroxotitanium aqueous solution concentration, maximum height roughness). The smaller the fluidity (seconds / 50 g), the better the fluidity, and “◎ (good)” means that the fluidity flows at 40 seconds / 50 g or less, and “◯ (good)” means fluidity even though the fluidity exceeds 40 seconds / 50 g. (Yes) ”, and“ × (No) ”for those that do not flow. Here, only“ ◎ (Good) ”was accepted in consideration of the molding processability by the powder metallurgy method.
表１には示していないが、粒子径がＤ90で２００μｍであると、粒子表面の酸化処理がなくても、流動度が２５秒／５０ｇ程度の流動性が確保される。 Although not shown in Table 1, when the particle diameter is D 90 and 200 μm, fluidity with a fluidity of about 25 seconds / 50 g is ensured even if the particle surface is not oxidized.
しかしながら、表１から分かるように、粒子径がＤ90で１００μｍになると、粉末の流動が困難となる。そこで、粒子表面の最大高さ粗さを３０ｎｍにすると、流動性が一気に合格レベルに改善される。粒子表面の最大高さ粗さを更に大きくして９５ｎｍにすると、流動性は更に改善される。ただし、粒子表面の最大高さ粗さが２１０ｎｍになると、逆に流動性が低下し、合格レベルを下回る。粒子径がＤ90で３５μｍの場合は、粒子径がＤ90で１００μｍの場合に比べると、流動性が若干低下するものの同様の傾向を示す。 However, as can be seen from Table 1, when the particle diameter is 100 μm at D 90 , powder flow becomes difficult. Therefore, when the maximum height roughness of the particle surface is set to 30 nm, the fluidity is improved to an acceptable level all at once. When the maximum height roughness of the particle surface is further increased to 95 nm, the fluidity is further improved. However, when the maximum height roughness of the particle surface is 210 nm, on the contrary, the fluidity is lowered and falls below the acceptable level. When the particle diameter is D 90 and 35 μm, the same tendency is shown although the fluidity is slightly lowered as compared with the case where the particle diameter is D 90 and 100 μm.
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